Soft Condensed Matter
Unveiling the CO2 Hydrate Phase Diagram from Computer Simulation: Locating the Hydrate-Liquid-Vapor Coexistence and its Upper Quadruple Point
Jesús Algaba, Samuel Blazquez, Cristóbal Romero-Guzmán et al. (+3 more)
Carbon dioxide (CO2) hydrates hold promising applications in capturing and separating CO2 for
climate change mitigation. Understanding their behavior at the molecular level is therefore essential, and computer simulations have become powerful tools for exploring their formation and stability, providing valuable insights into their underlying mechanisms. In this work, we perform molecular dynamics simulations to compute the three-phase coexistence line involving the stability region where CO2 is in the vapor phase: CO2 hydrate -
liquid water - vapor. This computation was previously inaccessible using the traditional three-phase direct coexistence technique. To achieve this, we employ a novel solubility-based method, which allows us to accurately evaluate the coexistence line. Finally, we have determined the upper quadruple point (Q2) where the four phases, namely hydrate,
liquid water,
liquid CO2, and vapor, coexist. Our pioneering result for the Q2 value shows remarkable agreement with experimental observations, validating the accuracy of our findings and representing a significant milestone in the field of gas hydrate research.
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All authors Jesús Algaba, Samuel Blazquez, Cristóbal Romero-Guzmán, Carlos Vega, María M. Conde, Felipe J. Blas
Mesoscale and Nanoscale Physics
Effect of hybrid field coupling in nanostructured surfaces on anisotropic signal detection in nanoscale infrared spectroscopic imaging methods
Ayona James, Maryam Ali, Zekai Ye et al. (+21 more)
Anisotropic intensity distributions on nanostructured surfaces and polarization-sensitive spectra have been observed in a number of nanoscale infrared spectroscopic imaging methods, including nano-FTIR [Bakir et al., Molecules, 2020, 25, 4295], photothermal induced resonance (PTIR) [Waeytens et al., Analyst, 2021, 146], tapping AFM-IR [Hondl et al., ACS Meas. Sci. Au, 2025, 5, 469; Luo et al., APL, 2022, 121, 23330], infrared photoinduced force microscopy (PiF-IR) [Anindo et al., JPCC, 2025, 129, 4517; Shcherbakov et al., Rev Methods Primers, 2025, 5, 1; Ali et al., Anal. Chem., 2025, 97, 23914] and peak force infrared microscopy (PFIR) [Xie et al., JPCC, 2022, 126, 8393; Anindo, JPCC, 2025]. A recent work combining modeling and experiment demonstrated that the hybrid field coupling of the IR illumination E0 with a
polymer nanosphere and a metallic AFM probe is nearly as strong as the plasmonic coupling in case of a gold nanosphere [Anindo, JPCC, 2025]. For p-polarized illumination, this results in enhanced IR absorption on the surface perpendicular to the propagation of E0 which can explain the observed anisotropic intensity distribution. An additional anisotropy may be introduced by aligned surface molecules with oriented vibrational transition moments [Bakir et al., Molecules, 2020, 25, 4295; Luo, APL, 2022]. PiF-IR is strongly surface sensitive combining an unprecedented spatial resolution < 5 nm with high spectral resolution [Shcherbakov, Rev Methods Primers, 2025; Ali, Anal. Chem., 2025], which allows, for example, to visualize nanoscale chemical variation on the surface of bacteria
cells affected by antimicrobial interaction [Ali, Anal. Chem., 2025]. We compare PiF-IR hyperspectra of aligned perylene Langmuir Blodgett monolayers on nanostructured and planar gold substrates and use
quantum chemical calculations of the oriented vibrational oscillators to interpret the observations.
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All authors Ayona James, Maryam Ali, Zekai Ye, Phan Thi Yen Nhi, Sharon Xavi, Mashiat Huq, Sajib Barua, Meng Luo, Yisak Tsegazab, Anna Elmanova, Robin Schneider, Olga Ustimenko, Sarmiza-Elena Stanca, Marco Diegel, Andrea Dellith, Uwe Hübner, Christoph Krafft, Jasmin Finkelmeyer, Maximilian Hupfer, Kalina Peneva, Matthias Zeisberger, Christin David, Martin Presselt, Daniela Täuber
Materials Science
Phonon-induced electronic degeneracy breaking: a SSAdNDP interpretation
Javiera Cabezas-Escares, Andrea Echeverri, Francisco Muñoz et al. (+1 more)
This work explores how
phonon perturbations can induce the breaking of electronic degeneracies near the
Fermi level and how this response can be interpreted from a chemical perspective through the SSAdNDP method. We apply this approach to a family of structurally similar yet electronically distinct hexagonal materials-MgB2,
graphene, and hBN-to analyze how a single
phonon mode simultaneously modifies the electronic structure (band dispersion) and the nature of chemical bonding (natural occupations and nodal patterns) in real space. Our results show that band splitting becomes physically relevant only when it is accompanied by an electronic redistribution, reflected in changes of the occupation numbers or bonding
topology. Thus, SSAdNDP provides a direct bridge between reciprocal- and real-space representations, translating phenomena such as electron-
phonon coupling into chemically intuitive reorganizations of multicenter bonds, and offering a unified framework to interpret vibrationally driven electronic effects in solids.
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All authors Javiera Cabezas-Escares, Andrea Echeverri, Francisco Muñoz, Anastassia N. Alexandrova
Superconductivity
Magnetism of the alternating monolayer-trilayer phase of La$_3$Ni$_2$O$_7$
Rustem Khasanov, Thomas J. Hicken, Hubertus Luetkens et al. (+9 more)
Understanding the
magnetic ground state of Ruddlesden-Popper nickelates is crucial, as these materials exhibit superconductivity under high pressure and host competing electronic orders that may play a key role in the pairing mechanism. In this work, we investigate the
magnetic properties of the alternating monolayer-trilayer phase of La$_3$Ni$_2$O$_7$ (1313-La$_3$Ni$_2$O$_7$) using
muon-
spin rotation/relaxation ($\mu$SR) under both ambient and hydrostatic pressure conditions. The monolayer-trilayer phase develops incommensurate
magnetic order below approximately 150 K, with a mean ordering temperature of $T_{SDW} \simeq 123$ K and a transition width of $\Delta T_{SDW} \simeq 15$ K. The abrupt onset of the internal
magnetic field indicates a first-order-like transition. Hydrostatic pressure ($p$) suppresses the
magnetic ordering temperature at a rate of $dT_{SDW}/d p \simeq -3.9$ K/GPa, demonstrating a progressive destabilization of the ordered state. By comparison with the
bilayer 2222-La$_3$Ni$_2$O$_7$ and the trilayer 3333-La$_4$Ni$_3$O$_{10}$ systems, and within a unified phenomenological framework, systematic trends are identified linking the pressure dependence of $T_{SDW}$, the (in)commensurability of the
magnetic order, and the character of the
magnetic transition. These trends consistently indicate a gradual reduction of electronic correlation strength from the
bilayer to the monolayer-trilayer and trilayer nickelates. This hierarchy suggests that the higher superconducting transition temperature observed in the 2222 phase may be closely connected to its more strongly correlated electronic nature. These results position the alternating monolayer-trilayer 1313-La$_3$Ni$_2$O$_7$ as an intermediate member linking the
magnetic behavior of the
bilayer 2222-La$_3$Ni$_2$O$_7$ and the trilayer 3333-La$_4$Ni$_3$O$_{10}$ Ruddlesden-Popper compounds.
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All authors Rustem Khasanov, Thomas J. Hicken, Hubertus Luetkens, Zurab Guguchia, Dariusz J. Gawryluk, Vignesh Sundaramurthy, Abhi Suthar, Masahiko Isobe, Bernhard Keimer, Giniyat Khaliullin, Matthias Hepting, Pascal Puphal
Materials Science
Thermal Equilibrium Vacancy Concentration in an Alloy with Chemical Short-Range Order
Hao Tang, Hoje Chun, Rafael Gomez-Bombarelli et al. (+2 more)
The
equilibrium vacancy concentration in multi-principal element
alloys remains a controversial and nontrivial subject, primarily because of chemical complexity and chemical short-range order (CSRO). Here we derive an exact expression that is amenable to atomistic calculations, using multiple perspectives. We applied this expression to equiatomic CrCoNi
alloys in the face-centered cubic structure. The derived
equilibrium vacancy concentration is used in our recent work, which predicts the chemical short-range order formation timescale consistent with experimental observation. The results demonstrate the practical utility of the approach for predicting
equilibrium vacancy concentrations in compositionally complex
alloys.
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All authors Hao Tang, Hoje Chun, Rafael Gomez-Bombarelli, Yuri Mishin, Ju Li
Mesoscale and Nanoscale Physics
A scanning probe microscopy approach for identifying defects in aluminum oxide
Leah Tom, Zachary J. Krebs, Joel B. Varley et al. (+8 more)
The coherence of
quantum dot
qubits fabricated in
semiconductors is often limited by charge noise from defects in gate dielectrics, which are material- and process-dependent. Characterizing these defects is an important step towards reducing their impact and improving
qubit coherence. The identification of individual defects requires atomic-scale spatial resolution, however, and sufficient spectral sensitivity to determine their electronic structure. Electrostatic force microscopy (EFM) provides highly resolved maps of the surface potential of dielectrics, and importantly, is also sensitive to single-electron charging processes that reflect the spectral structure of underlying defects. In this work, we use cryogenic EFM to characterize aluminum
oxide grown by atomic layer deposition (ALD) on bulk silicon. These measurements reveal defects close to the surface that exchange electrons with the EFM tip as they transition through different charge states. Detailed electrostatic modeling opens the door to powerful techniques for mapping tip-backgate charging voltages onto defect transition energies, allowing defects such as aluminum vacancies, and carbon, oxygen, or hydrogen
impurities to be identified, by comparing to density functional theory (DFT). These results point towards EFM as a powerful tool for exploring defect structures in solid-state
qubits.
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All authors Leah Tom, Zachary J. Krebs, Joel B. Varley, E. S. Joseph, Wyatt A. Behn, M. A. Eriksson, Keith G. Ray, Vincenzo Lordi, S. N. Coppersmith, Victor W. Brar, Mark Friesen
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Casimir Arc Plate Geometry: Computational Analysis of Thickness Constraints for Gold and Silver Nanomembranes in MEMS Applications
Anna-Maria Alexandrova and Jesus Valdiviezo
A theoretical analysis of the Casimir interaction between an arc and plate is conducted, which remains unexplored despite its relevance to Micro-Electro-Mechanical Systems (MEMS) fabrication. The configuration consists of a rigid finite plate and a flexible curved nanomembrane, with radius 100 micrometers, initially concave toward the rigid plate. The maximum thickness is evaluated for which the nanomembrane undergoes a change in
curvature: from concave to convex with respect to the plate, due to the Casimir interaction. The Casimir energy for a curved surface is derived using the Proximity Force Approximation (PFA) with next-to-leading-order (NTLO) corrections. Kirchhoff-Love theory for a thin isotropic plate of constant thickness is used to estimate the bending energy. Material-dependent effects on the Casimir interaction are evaluated by comparing Au and Ag plates. The maximum thickness is derived where U_Casimir > U_bending for distances in the range of 0.1-1 micrometers. Results show
curvature reversal occurs for nanomembranes with nanoscale thicknesses at the studied distances. Silver nanomembranes tolerate greater thickness than gold nanomembranes due to material-dependent properties. Comparison between NTLO-corrected PFA and perturbative PFA confirms the accuracy of the NTLO approach. The Casimir arc-to-plate geometry in MEMS enables Casimir-based actuation, enhances devices reliability, and prevents stiction. These findings provide thickness constraints for MEMS design and performance, accounting for the Casimir force.
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Quantum Gases · Cross-listed from physics.atom-ph
Magneto-Optical Trapping of a Metal Hydride Molecule
Jinyu Dai, Benjamin Riley, Qi Sun et al. (+2 more)
We demonstrate a three-dimensional magneto-optical trap (MOT) of a metal hydride molecule, CaH. We are able to scatter $\sim$$10^{4}$
photons with vibrational loss covered up to vibrational
quantum number $\nu=2$. This allows us to
laser slow the molecular beam near zero velocity with a "white-light" technique and subsequently load it into a
radio-frequency MOT. The MOT contains $230(40)$ molecules, limited by beam source characteristics and predissociative loss of CaH. The temperature of the MOT is below one millikelvin. The predissociative loss mechanism could, in turn, facilitate controlled dissociation of the molecule, offering a possible route to optical trapping of hydrogen atoms for precision spectroscopy.
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All authors Jinyu Dai, Benjamin Riley, Qi Sun, Debayan Mitra, Tanya Zelevinsky
Mesoscale and Nanoscale Physics
Xinghai Zhang, Ziyan Zhu, Justin H. Wilson et al. (+1 more)
Twisted multilayer moiré materials are generically quasiperiodic on the moiré scale due to the interference of different misaligned moiré periodicities. Spatial inhomogeneities such as these can be detrimental to superconductivity; nonetheless, superconductivity has been observed in quasiperiodic twisted trilayer
graphene (TTG). Here, we systematically study the superconducting properties of TTG. We reveal that an interplay between quasiperiodicity and
topology drives TTG into a critical regime, enabling it to host superconductivity with rigid phase stiffness for a wide range of twist angles, rather than at a fine-tuned value. The criticality in the normal state is due to the Dirac
fermions coupled by quasiperiodic tunneling simulating 3D topological
superconductor surface states. This critical-metal regime is marked by multifractal wave functions across the spectrum and scale-invariant transport reminiscent of the integer
quantum Hall plateau transition. We demonstrate this with large-scale wave function and Kubo conductivity calculations. These observations lead to a clear experimental implication: stronger interlayer coupling in TTG further stabilizes both the criticality and superconductivity, allowing superconductivity to be seen across a wider range of angles with experimentally accessible pressures.
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All authors Xinghai Zhang, Ziyan Zhu, Justin H. Wilson, Matthew S. Foster
Materials Science
Interface Modeling of Perovskite Polymer Heterostructures for Enhanced Charge Transfer Efficiency in Hybrid Photovoltaic Materials
Somayyeh Alidoust and V. Ongun Özçelik
Perovskite
solar cells (PSCs) based on methylammonium lead iodide (MAPbI3) exhibit remarkable photovoltaic performance, where interface engineering with hole transport layers (HTLs) is crucial for optimizing charge transfer and device efficiency. In this work, we present a density functional theory (DFT) study of the MAPbI3/poly(3-hexylthiophene) (P3HT) hybrid interface, focusing on the role of perovskite surface termination in determining interfacial stability and electronic structure. We model MAI- and PbI-terminated MAPbI3 surfaces interfaced with P3HT and compare their interfacial electronic properties. Electronic structure calculations reveal distinct differences in orbital hybridization and band
alignment: the MAI/m-P3HT interface exhibits weak coupling, whereas the PbI/m-P3HT interface shows stronger hybridization and enhanced charge transfer. Band
alignment confirms type-II, hole-selective character in both cases, with more pronounced valence band maximum adjustment for PbI. Charge difference maps, Bader analysis, and local density of states consistently indicate higher charge transfer and stronger electronic coupling for PbI termination. Electrostatic potential offsets and transport parameters further highlight termination-dependent differences, with lighter effective masses at PbI/m-P3HT and higher hole velocity at MAI/m-P3HT. These findings provide theoretical insight into interfacial charge transport mechanisms and offer guidelines for optimizing perovskite-organic hybrid
solar cells.
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Strongly Correlated Electrons
Magnetic and Transport Studies of the TbAgAl compound at high fields
Ashwin Mohan and Radha S
In order to further investigate the
magnetic state of the RAgAl series, the magnetization measurements on the TbAgAl compound from this series have been extended to higher fields of 12 Tesla in the temperature range 2K-300K. The electrical resistivity in the temperature range 2-300K has been measured up to fields of 9 Tesla. The field dependence of magnetization at low temperatures suggests an
antiferromagnetic state undergoing a metamagnetic transition to a
ferromagnetic state above the critical field. The observation of large coercivity (unlike other compounds in the RAgAl series) and non-saturation of magnetization indicates a disordered
magnetic state having both
ferromagnetic and
antiferromagnetic exchange interaction. The presence of competing interactions leading to a disordered state is also supported by transport measurements and is attributed presumably to the layered structure of the compound.
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Disordered Systems and Neural Networks · Cross-listed from quant-ph
Information Critical Phases under Decoherence
Akash Vijay and Jong Yeon Lee
Quantum critical phases are extended regions of phase space characterized by a diverging correlation length. By analogy, we define an information critical phase as an extended region of a mixed state phase diagram where the Markov length, the characteristic length scale governing the decay of the conditional mutual information (CMI), diverges. We demonstrate that such a phase arises in decohered $\mathbb{Z}_{N}$ toric codes by assessing both the CMI and the coherent information, the latter quantifying the robustness of the encoded logical qudits. For $N>4$, we find that the system hosts an information critical phase intervening between the decodable and non-decodable phases where the coherent information saturates to a fractional value in the thermodynamic limit, indicating that a finite fraction of logical information is still preserved. We show that the density
matrix in this phase can be decomposed into a convex sum of Coulombic pure states, where gapped anyons reorganize into gapless
photons. We further consider the ungauged $\mathbb{Z}_{N}$ toric code and interpret its mixed state phase diagram in the
language of strong-to-weak spontaneous
symmetry breaking. We argue that in the dual model, the information critical phase arises because the spontaneously broken off-diagonal $\mathbb{Z}_{N}$
symmetry gets enhanced to a $U(1)$
symmetry, resulting in a novel superfluid phase whose gapless modes involve coherent excitations of both the system and the environment. Finally, we propose an optimal decoding protocol for the corrupted $\mathbb{Z}_{N}$ toric code and show that its logical error rate saturates to a fractional value in the information critical phase. Our findings identify a gapless analog for mixed-state phases that still acts as a fractional topological
quantum memory, thereby extending the conventional paradigm of
quantum memory phases.
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Statistical Mechanics · Cross-listed from quant-ph
Charge-Informed Quantum Error Correction
Vlad Temkin, Zack Weinstein, Ruihua Fan et al. (+2 more)
We investigate the statistical physics of
quantum error correction in ${\rm U}(1)$
symmetry-enriched topological
quantum memories. Starting from a phenomenological error model of charge-conserving noise, we study the optimal decoder assuming the local charges of each anyon can be measured. The error threshold of the optimal decoder corresponds to a continuous phase transition in a disordered two-dimensional integer loop model on the Nishimori line. Using an effective replica field theory analysis and Monte Carlo numerics, we show that the optimal decoding transition exhibits Berezinskii-Kosterlitz-Thouless universality with a modified universal jump in winding number variance. We further generalize the model beyond the Nishimori line, which defines a large class of suboptimal decoders. At low nonzero temperatures and strong disorder, we find numerical evidence of a disorder-dominated loop-glass phase which corresponds to a "confidently incorrect" decoder. The zero-temperature limit defines the minimum-cost flow decoder, which serves as the ${\rm U}(1)$ analog of minimum-weight perfect matching in $\mathbb{Z}_2$ topological codes. Both the optimal and minimum-cost flow decoders are shown to dramatically outperform the charge-agnostic optimal decoder in
symmetry-enriched topological codes.
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All authors Vlad Temkin, Zack Weinstein, Ruihua Fan, Daniel Podolsky, Ehud Altman
Quantum Gases · Cross-listed from quant-ph
General Construction of Quantum Error-Correcting Codes from Multiple Classical Codes
Yue Wu, Meng-Yuan Li, Chengshu Li et al. (+1 more)
The hypergraph product (HGP) construction of
quantum error-correcting codes (QECC) offers a general and explicit method for building a QECC from two classical codes, thereby paving the way for the discovery of good
quantum low-density parity-check codes. In this letter, we propose a general and explicit construction recipe for QECCs from a total of D classical codes for arbitrary D. Following this recipe guarantees the obtainment of a QECC within the stabilizer formalism and nearly exhausts all possible constructions. As examples, we demonstrate that our construction recovers the HGP construction when D = 2 and leads to four distinct types of constructions for D = 3, including a previously studied case as one of them. When the input classical codes are repetition codes, our D = 3 constructions unify various three-dimensional
lattice models into a single framework, encompassing the three-dimensional toric code model, a fracton model, and two other intriguing models not previously investigated. Among these, two types of constructions exhibit a trade-off between code distance and code dimension for a fixed number of
qubits by adjusting the lengths of the different classical codes, and the optimal choice can simultaneously achieve relatively large values for both code distance and code dimension. Our general construction protocol provides another perspective for enriching the structure of QECCs and enables the exploration of richer possibilities for good codes.
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All authors Yue Wu, Meng-Yuan Li, Chengshu Li, Hui Zhai
Materials Science
Keffer-like form of the symmetric Heisenberg exchange integral: Contribution to the Landau–Lifshitz–Gilbert equation and spin wave dispersion dependence
Pavel A. Andreev
The symmetric Heisenberg exchange interaction and antisymmetric Dzyaloshinskii-Moriya interaction are parts of the tensor potential describing effective
spin-
spin interaction caused by the superexchange interaction of
magnetic ions via nonmagnetic ion. There is the Keffer form of the vector constant of the Dzyaloshinskii-Moriya interaction, which includes the shift of the nonmagnetic ion (ligand) from the line connecting two
magnetic ions. It is suggested, in this paper, that the ligand shift can give contribution in the constant of the symmetric Heisenberg interaction in
antiferromagnetic or ferrimagnetic materials. Hence, the constant of the Heisenberg interaction is composed minimum of two terms. One does not depend on the ligand shift an gives standard contribution in the energy density like term with no derivatives of the
spin densities or term containing two spatial derivatives of the
spin densities. It is demonstrated that additional term gives a term in the energy density containing one spatial derivative of the
spin density. Corresponding contribution in the Landau–Lifshitz–Gilbert equation is found. Possibility of the noncollinear
equilibrium order of
spin under influence of new
spin torque is discussed. Modification of the
spin wave (normal modes) dispersion dependencies in the
antiferromagnetic materials is found for the collinear order and for the cycloidal order of
spins. Effective
spin current is derived and applied for the
spin-current model of the polarization origin in multiferroics.
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Quantum Gases
Effect of Population Imbalance on Vortex Mass in Superfluid Fermi Gases
Lucas Levrouw, Hiromitsu Takeuchi and Jacques Tempere
One of the fundamental parameters associated with quantized
vortices in superfluids is the
vortex mass, which is the inertia of a
vortex. As of yet, this mass has not been observed in a superfluid. However, ultracold
Fermi gases provide a promising platform in which recently much experimental progress was made, offering tunability of the interaction as well as control on the single-
vortex level. Not only can the scattering length be freely tuned, allowing exploration of the BEC-BCS crossover, but also an imbalance between different pseudospin states can be introduced. We study the effect of introducing this imbalance on the
vortex mass, using a method based on an effective field theory for superfluid
Fermi gases. We find that it is crucial to consider the imbalance in conjunction with nonzero temperatures; at some temperatures, the
vortex mass is significantly enhanced while at others, the
vortex mass is diminished. This pronounced temperature dependence highlights the need for careful tuning of experimental conditions and identifies favorable parameter regimes in which the
vortex mass is likely to be observed.
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Disordered Systems and Neural Networks
A Minimal Network of Brain Dynamics: Hierarchy of Approximations to Quasi-critical Neural Network Dynamics
Jeremy B. Goetz, Naruepon Weerawongphrom, Rashid V. Williams-García et al. (+2 more)
We present an interacting model of neural network dynamics that incorporates key biological features, including multiple forms of inhibitory interactions. We develop a hierarchy of analytical mean-field approximations to characterize nonequilibrium phase transitions between ordered, disordered, and chaotic regimes, complemented by a detailed stability analysis. We show that inhibition generically enhances the stability of network dynamics. The model is consistent with the quasi-criticality hypothesis, exhibiting regions of maximal dynamical susceptibility and mutual information, modulated by the strength of external stimuli. We further demonstrate that, at the mean-field level, the critical transition belongs to the mean-field directed percolation universality class, in agreement with prior experimental and theoretical studies. More broadly, our framework may offer insights into neurological disorders, with the unstable regime exhibiting chaotic dynamics that may be associated with epileptic seizures.
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All authors Jeremy B. Goetz, Naruepon Weerawongphrom, Rashid V. Williams-García, John M. Beggs, Gerardo Ortiz
Materials Science
Unlocking klockmannite: formation of colloidal quasi-2D CuSe nanocrystals and photo-physical properties arising from crystal anisotropy
Urvi Parekh, Nadiia Didukh, Samira Dabelstein et al. (+8 more)
Copper selenide is an exceptional quasi-layered monolithic material that exhibits both semiconducting and metallic properties in adjacent visible and near-infrared (NIR) spectral ranges. Here we introduce a thiol-free colloidal synthesis for generating quasi-2D klockmannite copper selenide nanocrystals via hot injection method, achieving shape control by tuning the injection temperature and precursor concentrations without any additional ligands. This approach produces large klockmannite nanosheets with lateral sizes from 200 nm to several micrometres, as well as uniform triangular nanoplatelets with sizes of 12-25 nm that are monocrystalline and display strong NIR plasmonic absorption. The spectral features of the anisotropic klockmannite phase in the NIR have been analysed using complex-scaled discrete dipole approximation (CSDDA) calculations, which reveal pronounced optical anisotropy and the emergence of
hyperbolic regime. The combined effect of propagating and evanescent fields is regarded as the underlying reason of such modes in the
hyperbolic domain. Finally, the ultrafast photophysical behaviour of the material in klockmannite phase is examined, including hot-hole cooling, trapping, and coherent
phonons generation. Our findings emphasize the important role of the intrinsic
crystal anisotropy in governing the physical properties of nanoscale klockmannite.
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All authors Urvi Parekh, Nadiia Didukh, Samira Dabelstein, Ronja Piehler, Eugen Klein, Jivesh Kaushal, Tobias Korn, Stefan Lochbrunner, Christian Klinke, Stefan Scheel, Rostyslav Lesyuk
Mesoscale and Nanoscale Physics
Ferroelectricity in a magnon Bose-Einstein condensate: Nonreciprocal superfluidity, exceptional points, and Majorana bosons
Kazuki Yamamoto, Takuto Kawakami and Mikito Koshino
We investigate a ferroelectric instability of a
magnon Bose-Einstein condensate, mediated by its interaction with an electric field through a
geometric Aharonov-Casher (AC) phase. A distinct feature of the system is the positive feedback loop in which an electric field induces
magnon orbital motion via the AC phase, generating electric polarization that in turn enhances the original field. Based on bosonic Bogoliubov-de Gennes (BdG) mean-field theory, we show that this feedback drives a spontaneous ferroelectric transition in the
magnon superfluid, accompanied by a persistent
magnon supercurrent. In the resulting ferroelectric phase, the quasiparticle excitation spectrum becomes nonreciprocal, reflecting spontaneous breaking of spatial inversion
symmetry. At the critical point of the transition, the bosonic BdG
Hamiltonian exhibits a global coalescence of both
eigenvalues and eigenvectors, forming exceptional points throughout the entire Brillouin zone. The corresponding eigenvector is an equally weighted superposition of bosonic quasiparticle and quasihole states and is invariant under particle-hole transformation, allowing it to be interpreted as a bosonic analog of a Majorana
fermion.
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Mesoscale and Nanoscale Physics
Coherent Absorption Synergizes with Plasmon-Enhanced Graphene Terahertz Photo-thermoelectric Response
Runli Li, Shaojing Liu, Ximiao Wang et al. (+4 more)
Terahertz (THz) technology shows great potential in 6G communications and imaging, but faces challenges related to detector sensitivity, noise, and cryogenic operation. Here, we integrate interferometric enhancement of absorption (IEA) from a metal reflection layer with a
graphene plasmon polariton atomic cavity (PPAC)-based photodetector. The hybrid configuration enhances the in-plane electric field and improves the plasmon-induced thermal gradient. Numerical simulations and photoresponse measurements were employed to systematically investigate the influence of a metal reflective layer on the photothermoelectric behavior of the device, which reveals the IEA design significantly boosts the THz absorption rate in
graphene nanostructures and promotes asymmetry in the lateral
diffusion of hot carriers. Compared with the bare device, the responsivity of the device is enhanced by approximately 30-folds, while maintaining a response time below 130 microseconds. We further demonstrate the potential of the device to distinguish concealed
liquids, advancing high-responsivity, room-temperature, and compact terahertz imaging technology.
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All authors Runli Li, Shaojing Liu, Ximiao Wang, Hongjia Zhu, Yongsheng Zhu, Shangdong Li, Huanjun Chen
Materials Science
Spin Dynamics in the van der Waals Ferromagnet CrTe2 Engineered by Niobium Doping
Dhan Raj Lawati, Prem Bahadur Karki, Jitender Kumar et al. (+14 more)
Understanding and controlling
spin dynamics in two-dimensional (2D) van der Waals (vdW) ferromagnets is essential for their application in magnonics and hybrid
quantum platforms. Here, we investigate the
spin dynamics of the vdW ferromagnet 1T-CrTe_{2} and demonstrate their systematic tunability via niobium (Nb) substitution in Cr_{1-x}Nb_{x}Te_{2}(x=0-0.2).
Ferromagnetic resonance (FMR) spectroscopy reveals that Nb doping enables wide-band tuning of the resonance frequency from 40 GHz down to the few-GHz regime, accompanied by a moderate increase in the Gilbert damping constant from ~0.066 to ~0.14, while preserving robust room-temperature ferromagnetism. Complementary magnetometry shows a concurrent reduction of the Curie temperature and saturation magnetization with increasing Nb content. Density functional theory calculations attribute the observed
spin-dynamic trends to Nb-induced modifications of
magnetic anisotropy and
magnetic exchange interactions. Furthermore, CrTe_{2} flakes (~80 nm thick) exhibit lower resonance frequencies and damping than bulk
crystals, consistent with thickness, surface/interface, and shape-dependent
magnetic anisotropy. These results establish Nb-doped CrTe_{2} as a tunable vdW ferromagnet with controllable
spin dynamics, extending its functionality from spintronics to broadband magnonics and
quantum magnonics.
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All authors Dhan Raj Lawati, Prem Bahadur Karki, Jitender Kumar, Karishma Prasad, Mohamed A. Elekhtiar, Kai Huang, Bibek Tiwari, Suvechhya Lamichhane, Rupak Timalsina, Zane Hubble, Ayodimeji E. Aregbesola, John Watt, Sy-Hwang Liou, Evgeny Y. Tsymbal, Jian Wang, Kapildeb Ambal, Abdelghani Laraoui
Strongly Correlated Electrons
Non-reciprocal circular dichroism of axial phonons coupled to ferro-rotational order
H. Y. Huang, G. Channagowdra, D. Banerjee et al. (+10 more)
Circular dichroism (CD) in X-ray absorption, defined as the difference in absorption between opposite circular polarizations, is fundamentally enabled by the breaking of time-reversal
symmetry or inversion
symmetry. It is therefore sensitive to magnetism, chirality, and their interplay. In contrast, the sample
symmetry alone is insufficient to determine whether CD in resonant inelastic X-ray scattering (RIXS) is allowed. Rather, RIXS-CD is governed by both the sample
symmetry and the scattering geometry. Here, using RIXS, we identify circularly polarized
phonons coupled to ferro-rotational order in MnTiO$_3$, which we refer to as ferro-axial
phonons. Their excitations provide a direct demonstration of non-reciprocal RIXS-CD, in which the dichroic response changes upon reversing the propagation direction of the incident X-rays, although the system globally preserves both inversion and time-reversal
symmetries. We propose that a condensate of these
phonons, manifested as standing waves, underlies the ferro-rotational order in MnTiO$_3$. The observed non-reciprocal CD reflects the interplay among
photon helicity,
phonon polarization, and ferro-rotational order.
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All authors H. Y. Huang, G. Channagowdra, D. Banerjee, E. V. Komleva, J. Okamoto, C. T. Chen, M. Guennou, S. Johnston, S. V. Streltsov, C. Y. Mou, A. Fujimori, S-W. Cheong, D. J. Huang
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Towards an understanding of dipole-dipole interactions in nonlocal media
L. Inácio, A. Kurumbail, S. K. Panja et al. (+2 more)
We commence our study with review of dispersion interactions in electrolytes. We then reflect on how background media change atom-atom excited-state systems. To highlight the impact of nonlocal media, such as salt solutions, we predict that a new contribution to the resonance interaction energy emerges in a form $\propto e^{-\kappa_{\rm D} \rho}/\rho$. Here $\kappa_{\rm D}$ is the Debye length and $\rho$ is the distance between the atoms. This contribution vanishes at zero temperature, where a new term proportional to $1/\rho^4$ (similar to free space) occurs. This new term is dampened by the electrolyte at large distances, causing it to decrease much faster, proportional to $1/\rho^7$. The long-range electrolyte-induced resonance interaction at finite temperature may, in addition to the dominating van der Waals attraction (which goes as $1/\rho^6$), take part in the molecular formation of biological fluids.
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All authors L. Inácio, A. Kurumbail, S. K. Panja, I. Brevik, M. Boström
Statistical Mechanics
Site-Order Optimization in the Density Matrix Renormalization Group via Multi-Site Rearrangement
Ryo Watanabe, Toshiya Hikihara and Hiroshi Ueda
In the approaches based on
matrix-product states (MPSs), such as the density-
matrix renormalization group (DMRG) method, the ordering of the sites crucially affects the computational accuracy. We investigate the performance of an
algorithm that searches for the optimal site order by iterative local site rearrangement. We improve the
algorithm by expanding the range of site rearrangement and apply it to a one-dimensional
quantum Heisenberg model with random site permutation. The results indicate that increasing the range of the site rearrangement significantly improves the computational accuracy of the DMRG method. In particular, increasing the rearrangement range from two to three sites reduces the average relative error in the ground-state energy by 65% to 94% in the cases we tested. We also discuss the computational cost of the
algorithm and its application as a preprocessing for MPS-based calculations.
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Superconductivity
Necessary conditions for spin-resolved Josephson diode effect across strongly spin-polarized magnetic materials
Danilo Nikolić, Niklas L. Schulz and Matthias Eschrig
We present a set of necessary conditions for the appearance of charge and
spin Josephson diode effects across strongly
spin-polarized inhomogeneous
magnetic materials (FM) placed between two
spin-singlet
superconductors. Noncoplanarity of the FM's
spin texture gives rise to
quantum geometric phases, $\Delta\varphi'$, that enter the Josephson current-phase relation (CPR) similarly to the superconducting phase difference, resulting in charge and
spin Josephson diode effects. Our study shows that such effects appear if the CPR possesses no phase-inversion center, achieved under the following conditions. First, noncoplanarity of the
spin texture is necessary to break the spatial inversion
symmetry. Second, both
spin bands have to contribute to the transport, i.e., the effect is absent in half-metallic junctions. Third, different band-specific densities of states are required, and this condition is ensured by the strong
spin polarization of the FM. Finally, higher harmonics in the CPR are necessary, i.e., the effect is absent in the tunneling limit. However, even in this case, the CPR must not have a phase-inversion center, which is ensured by the restriction of the
quantum geometric phase to values $\Delta\varphi'\neq k\pi/2, k\in\mathbb{Z}$. We formulate a minimal phenomenological model that incorporates all these points, qualitatively illustrating our theory.
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Statistical Mechanics
Diffusion in Rugged Energy Landscapes in the Presence of Spatial Correlations : A Surprising Route to Zwanzig's Mean-Field Prediction
Biman Bagchi
Diffusion in rugged free-energy landscapes is central to diverse problems in chemical physics, biomolecular dynamics,
polymer transport and numerous disordered systems. Zwanzig's well-known classic mean-field theory predicts that roughness reduces the
diffusion coefficient by an exponential factor determined solely by the variance of the disorder. However, the numerical studies of Banerjee, Seki, and Bagchi (BSB) showed that this result fails for uncorrelated Gaussian-distributed site energies because rare but deep three-site traps dominate long-time transport. BSB introduced Gaussian spatial correlations - originally developed in astrophysics to model turbulent density fluctuations - and demonstrated that even modest correlations suppress these pathological traps and restore Zwanzig's exponential scaling. Here we present here a unified theoretical framework clarifying (i) why Zwanzig's local averaging, may be viewed as a Gaussian cumulant expansion, could breakdown. In particular, how its validity is destroyed by uncorrelated disorder, and (ii) how Gaussian spatial correlations reshape roughness increments, eliminate asymmetric multi-site traps, and thereby recover mean-field
diffusion, and (iii) a derivation showing exactly how Gaussian spatial correlations modify roughness increments, trap statistics, and ultimately the
diffusion constant. We also provide explicit numerical triplet examples illustrating the dramatic reduction of escape times produced by spatial correlations.
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Materials Science
Interplay between electronic and phononic energy dissipation channels in the adsorption of CO on Cu(110)
Carmen A. Tachino, Federio J. Gonzalez, Alberto S. Muzas et al. (+3 more)
In this work, we investigate the relative importance of electronic and phononic energy dissipation during the molecular adsorption of CO on Cu(110). Initial sticking probabilities as a function of impact energy for CO impinging at normal incidence at a surface temperature of 90 K were computed using classical trajectory simulations. To this aim, we use a full-dimensional potential energy surface constructed using an atomistic neural network trained on density functional theory data obtained with the nonlocal vdW-DF2 exchange-correlation functional. Two models are compared: one allowing only energy transfer and dissipation from the molecule to
lattice vibrations, and the other also incorporating the effect of molecular energy loss due to the excitation of electron-hole pairs, modeled within the local-density friction approximation. Our results reveal, firstly, that the molecule mainly transfers energy to
lattice vibrations, and this channel determines the adsorption probabilities, with electronic friction playing a minor role. Secondly, once the molecule is trapped near the surface (where electronic density is higher), electron-hole pair excitations accelerate energy dissipation, significantly promoting CO thermalization. Still, the faster energy dissipation when electron-hole pair excitations are accounted for accelerates the accommodation of the adsorbed molecules in the chemisorption well but does not significantly alter their lateral displacements over the surface.
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All authors Carmen A. Tachino, Federio J. Gonzalez, Alberto S. Muzas, J. Iñaki Juaristi, Maite Alducin, H. Fabio Busnengo
Materials Science
CO$_2$ Dissociative Sticking on Cu(110)
Federico J. Gonzalez, Carmen A. Tachino and H. Fabio Busnengo
In this work we investigate the dissociation of CO$_2$ on Cu(110) by performing density functional theory calculations using the vdW-DF2 exchange-correlation functional, with a potential energy surface parameterized using artificial neural networks. We computed quasi-classical trajectory calculations of molecular and dissociative adsorption probabilities as a function of the initial impact energy of the molecules and surface temperature, by comparing our results with available supersonic molecular beam experimental data for normal incidence. Concerning the general dependence of the molecular and dissociative adsorption probabilities on the initial translational energy of the molecules, our theoretical results agree with experiments. Also in agreement with experiments, we have found that dissociative adsorption is not affected by surface temperature between 50 and 400 K, for impact energies for which the dissociation probability is larger than $\sim 10^{-3}$. We have investigated the influence of impact energy and surface temperature on the final state of the dissociation products by extending the time integration of the reactive trajectories up to 10 ps. We have found that above $\sim 2.5$ eV and close to or above room temperature, CO$_2$ dissociation induces strong surface distortions including final structures involving Cu adatoms. The creation of Cu vacancy-adatom pairs is stimulated by the presence of both CO$_{ads}$ and O$_{ads}$ which interact strongly with the Cu adatoms and even give rise to unexpected (O-Cu-CO)$_{ads}$ linear moieties anchored to the surface by the dissociated O atom and involving a Cu adatom almost detached from the surface. These surface distortions produced by dissociation products of high energy CO$_2$ molecules at and above room temperature might explain recent experiments that have found a greater saturation oxygen coverage for high energy molecules.
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Disordered Systems and Neural Networks · Cross-listed from quant-ph
Spacetime Spins: Statistical mechanics for error correction with stabilizer circuits
Cory T. Aitchison and Benjamin Béri
A powerful method for analyzing
quantum error-correcting codes is to map them onto classical statistical mechanics models. Such mappings have thus far mostly focused on static codes, possibly subject to repeated syndrome measurements. Recent progress in
quantum error correction, however, has prompted new paradigms where codes emerge from stabilizer
circuits in spacetime – a unifying perspective encompassing syndrome extraction
circuits of static codes, dynamically generated codes, and logical operations. We show how to construct statistical mechanical models for stabilizer
circuits subject to independent Pauli errors, by mapping logical equivalence class probabilities of errors to partition functions using the spacetime subsystem code formalism. We also introduce a modular
language of
spin diagrams for constructing the
spin Hamiltonians, which we describe in detail focusing on independent
circuit-level X-Z error channels. With the repetition and toric codes as examples, we use our approach to analytically rank logical error rates and thresholds between code implementations with standard and dynamic syndrome extraction
circuits, describe the effect of transversal logical Clifford gates on logical error rates, and perform Monte Carlo simulations to estimate maximum likelihood thresholds. Our framework offers a universal prescription to analyze, simulate, and compare the decoding properties of any stabilizer
circuit, while revealing the innate connections between dynamical
quantum systems and noise-resilient phases of matter.
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Materials Science
Tunable Magnetic and Topological Phases in EuMnXBi$_2$ (X=Mn, Fe, Co, Zn) Pnictides
Deep Sagar, Abhishek Sharma and Arti Kashyap
We present a comprehensive density functional theory (DFT) study of the electronic,
magnetic, and topological properties of the layered pnictides EuMnXBi2 (X = Mn, Fe, Co, Zn), focusing in particular on the relatively unexplored Bi-based member of the EuMn2X2 family. Unlike the well-studied As-, Sb-, and P–based analogues, we show that EuMn2Bi2 stabilizes in a C-type
antiferromagnetic ground state with a narrow-gap semiconducting character. Inclusion of
spin-orbit coupling (SOC) drives a transition from this trivial
antiferromagnetic semiconductor to a Weyl semimetal hosting four
symmetry-related Weyl points and robust
Fermi arc states. Systematic substitution of Mn with Fe, Co, and Zn further reveals a tunable sequence of
magnetic ground states: Fe and Co induce ferrimagnetism with semimetallic behavior, while Zn stabilizes a
ferromagnetic semimetal with a large net moment. These findings establish Bi-based EuMnXBi2 pnictides as a versatile platform where
magnetic exchange interactions and band
topology can be engineered through SOC and chemical substitution. The complex interplay of
magnetic interactions and topological effects in the proposed bulk and doped pnictides opens a promising avenue to explore a wide range of electronic and
magnetic phenomena. In particular, this study demonstrates that EuMn2Bi2 hosts tunable
magnetic and topological phases driven by electron correlations, chemical substitution, and
spin-orbit coupling.
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