Statistical Mechanics · Cross-listed from hep-th
Clifford Solver for the Tetrahedron Equation and its Variants
Pramod Padmanabhan, Vivek Kumar Singh and Vladimir Korepin
The different forms of the tetrahedron equation appear when all possible ways to label the scattering process of infinitely long straight lines are considered in three dimensional spacetime. This is expected to lead to three dimensional integrability, analogous to the Yang-Baxter equation. Among the three possibilities, we consider two of them and their variants. We show that Clifford
algebras solve both the constant and the spectral parameter dependent versions of all of them. We also present a scheme for canonically solving higher simplex equations using tetrahedron solutions.
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Materials Science
Relativistic Spin-momentum locking in altermagnets
Carmine Autieri and Amar Fakhredine
Spin-momentum locking in altermagnets has been deeply explored in the non-relativistic limit. Including
spin-orbit coupling, altermagnets exhibit antisymmetric exchange interactions, leading to
spin cantings. Therefore, the
spin-momentum locking differs among the three
spin components Sx, Sy, and Sz, forming the relativistic
spin-momentum locking. We consider orthorhombic YVO3 and hexagonal MnTe. For YVO3, the relativistic locking comprises s-, dxy -, and dxz-wave. In MnTe, the dominant component Sy of MnTe inherits the polarized charge distribution and the non-relativistic
spin-momentum locking bulk g-wave, but the breaking of the C6z rotational
symmetry by the Neel vector lowers the
symmetry from g-wave to d-wave. The relativistic
spin-momentum locking for MnTe is composed of dxz-, dyz- and s-wave. Despite small magnitudes in real space, the canted
spin components contribute significant spectral weight in k-space, impacting k-space properties such as the
spin-
Hall conductivity.
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Materials Science
Thickness dependent rare earth segregation in magnetron deposited NdCo$_{4.6}$ thin films studied by Xray reflectivity and Hard Xray photoemission
J. Díaz, J. Rodríguez-Fernández and J. Rubio-Zuazo
Magnetic anisotropy in disordered rare-earth-transition metals (RE-TM) compounds arises from RE atoms occupying asymmetric environments within the TM
lattice. However, the underlying mechanism that promotes such environments remains not fully understood. In this study, we investigate amorphous NdCo$_{4.6}$ thin films deposited by magnetron sputtering, where the
magnetic anisotropy evolves with thickness from in-plane to out-of-plane orientation above 40 nm. X-ray reflectivity measurements revealed the progressive formation of an additional layer between the 3 nm Si capping layer and the NdCo film with increasing film thickness. To probe the composition and distribution of Co and Nd near the surface, Hard X-ray Photoemission Spectroscopy (HAXPES) was performed on films ranging from 5 nm to 65 nm in thickness using incident
photon energies of 7, 10, and 13 keV. These correspond to inelastic electron mean free paths of 7.2-12.3 nm in cobalt. The cobalt atomic concentration, deduced from HAXPES at the Nd 3d and Co 2p excitations, was consistently below the nominal value and varied with both thickness and
photon energy. This indicates segregation of RE atoms at the film surface, which becomes more pronounced with increasing thickness. Background analysis of the Co 2p and Nd 3d peaks supports this conclusion. The thickness of the Nd segregated layer is estimated in 2-3 nm. These findings demonstrate that incorporating neodymium into the cobalt
lattice incurs an energy cost which is associated with strain due to the volume mismatch between the two elements. Reducing this strain energy promotes anisotropic atomic environments for Nd, thereby explaining the emergence of perpendicular anisotropy and its dependence on film thickness in these RE-TM compounds.
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Soft Condensed Matter
Convective Flows in Sheared Packings of Spherical Particles
Mehran Erfanifam, Mahnoush Madani, Reza Shaebani et al. (+1 more)
Understanding how granular materials respond to shear stress remains a central challenge in soft matter physics. We report direct observations of persistent granular convection in the bulk shear zones of spherical particle packings – a phenomenon previously associated primarily with particle shape anisotropy or boundary effects. By employing various bead-coloring techniques in a split-bottom geometry, we reveal internal flow fields within sheared granular packings. We find robust convection rolls, strikingly governed by system geometry: at low filling heights, two counter-rotating convection rolls emerge, while at higher filling heights, a single dominant convection roll forms, featuring radially outward flow at the surface. This transition is driven by the height-dependent broadening of the shear zone, which introduces shear rate asymmetry across its flanks. Notably, the transition occurs entirely within the open shear band regime. These findings underscore the pivotal role of system geometry in shaping secondary flow formation in dense packings of frictional particles, suggesting possible broader relevance to geophysical flow dynamics and industrial applications.
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All authors Mehran Erfanifam, Mahnoush Madani, Reza Shaebani, Maniya Maleki
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
A Scalable Superconducting Circuit Framework for Emulating Physics in Hyperbolic Space
Xicheng Xu, Ahmed Adel Mahmoud, Noah Gorgichuk et al. (+3 more)
Theoretical studies and experiments in the last six years have revealed the potential for novel behaviours and functionalities in device physics through the synthetic engineering of negatively-curved spaces. For instance, recent developments in
hyperbolic band theory have unveiled the emergence of higher-dimensional eigenstates – features fundamentally absent in conventional Euclidean systems. At the same time, superconducting
quantum circuits have emerged as a leading platform for
quantum analogue emulations and digital simulations in scalable architectures. Here, we introduce a scalable superconducting
circuit framework for the analogue
quantum emulation of tight-binding models on
hyperbolic and kagome-like
lattices. Using this approach, we experimentally realize three distinct
lattices, including, for the first time to our knowledge, a
hyperbolic lattice whose unit
cell resides on a genus-3 Riemann surface. Our method encodes the
hyperbolic metric directly into capacitive couplings between high-quality superconducting resonators, enabling tenable reproduction of spectral and localization properties while overcoming major scalability and spectral resolution limitations of previous designs. These results set the stage for large-scale experimental studies of
hyperbolic materials in condensed matter physics and lay the groundwork for realizing
hyperbolic quantum processors, with potential implications for both fundamental physics and
quantum computing
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All authors Xicheng Xu, Ahmed Adel Mahmoud, Noah Gorgichuk, Ronny Thomale, Steven Rayan, Matteo Mariantoni
Materials Science
Stress in chromium thin films deposited by DC magnetron sputtering on grounded cupper and stainless-steel substrate holders
M.D. Medina, H.I. Giron, K. Paucar et al. (+2 more)
Chromium thin films deposited on silicon substrates by DC magnetron sputtering were systematically investigated as a function of film thickness, using a DC power of 50 W and a post-deposition annealing temperature of 200 C. Two types of grounded substrate holders, copper and stainless steel, were employed to assess substrate-dependent effects. The intrinsic stress, determined by the wafer
curvature method, decreases with increasing film thickness but increases with the annealing temperature. It is observed that for thinner as-deposited chromium films, the stress showed a pronounced irreversible increase when measured immediately after deposition and after several days of aging. Films deposited on copper holders consistently exhibited higher stress values than those grown on stainless steel holders. These observations suggest that the intrinsic stress in as-deposited films is linked to the growth mechanism, while the stress increase after annealing may be related to thermally active
diffusion and structural relaxation. The higher stress in films grown on copper substrate holder can likely be associated with enhanced ion bombardment due to the higher electrical conductivity of copper.
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All authors M.D. Medina, H.I. Giron, K. Paucar, A. Talledo, B.R. Pujada
Superconductivity
Observation of a pronounced Hebel-Slichter peak in the spin-lattice relaxation rate and implications for gap and pairing symmetry in LaNiGa$_2$
P. Sherpa, R. Hingorani, A. Menon et al. (+11 more)
We report a pronounced Hebel-Slichter coherence peak in the zero field
nuclear quadrupolar resonance (NQR)
spin-
lattice relaxation rate of the topological crystalline
superconductor LaNiGa$_2$ in the superconducting state. Previously, a two-band internally antisymmetric non-
unitary triplet pairing (INT) state was proposed for this system, with equal
spin-pairing and two distinct gaps associated with different
spins. A detailed examination of the temperature dependence of the NQR data shows that the data best fit an INT model if the two gaps are equal and the model is
unitary. Even a tiny non-unitarity with two unequal gaps causes the coherence peak to diminish rapidly and deviate from the data. On the other hand, the data are well-fit by a two-band singlet BCS-like pairing with two distinct gaps consistent with previous measurements. This raises doubts on the identification of non-
unitary triplet-pairing with time-reversal
symmetry breaking in this material.
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All authors P. Sherpa, R. Hingorani, A. Menon, I. Vinograd, C. Chaffey, A. P. Dioguardi, R. Yamamoto, M. Hirata, F. Ronning, J. R. Badger, P. Klavins, R. R. P. Singh, V. Taufour, N. J. Curro
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Spectrally Robust Photon-Pair Generation in Topological Waveguide Arrays
A. Zecchetto, J.-R. Coudevylle, M. Morassi et al. (+4 more)
Harnessing topological effects offers a route to protect
quantum states of light from imperfections, potentially enabling more robust platforms for
quantum information processing. This capability is particularly relevant for active photonic
circuits that generate
quantum light directly on-chip. However, the impact of
topology on the spectral properties of parametric processes, crucial for scalable
quantum photonic
circuits, remains largely unexplored. Here, we address this question by investigating
photon-pair generation via spontaneous parametric down-conversion (SPDC) in nonlinear waveguide arrays, combining experiment and theory. A systematic comparison of uniform, trivial, and topological Su-Schrieffer-Heeger (SSH) arrays reveals that only the topological configuration preserves a stable SPDC resonance spectrum under coupling disorder, with fluctuations in the resonance wavelength reduced by more than an order of magnitude. An analytical model captures the origin of this robustness in the band-structure properties of the interacting modes. Numerical analysis further shows that each SSH array can operate as a robust
photon-pair source, enabling stable interference between multiple such sources and the generation of high-dimensional entangled states with high fidelity. These results establish nonlinear waveguide arrays as a promising platform for harnessing the interplay of
topology and nonlinearity in
quantum photonic
circuits.
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All authors A. Zecchetto, J.-R. Coudevylle, M. Morassi, A. Lemaître, M.I. Amanti, S. Ducci, F. Baboux
Mesoscale and Nanoscale Physics
Metallic Electro-Optic Effect in Twisted Double-Bilayer Graphene
D. J. P. de Sousa, N. Roldan-Levchenko, C. O. Ascencio et al. (+3 more)
Recent theoretical advances have highlighted the role of Bloch state intrinsic properties in enabling unconventional electro-optic (EO) phenomena in bulk metals, offering novel strategies for dynamic optical control in
quantum materials. Here, we identify an alternative EO mechanism in bulk metallic systems that arises from the interplay between Berry
curvature and the orbital
magnetic moment of Bloch electrons. Focusing on twisted double-
bilayer graphene (TDBG), we show that the enhanced intrinsic properties of moiré Bloch bands give rise to a sizable linear magnetoelectric EO response, a first-order, electric-field-induced non-Hermitian correction to the gyrotropic
magnetic susceptibility. This mechanism dominates in $C_{3z}$-symmetric TDBG, where EO contributions originating from the Berry
curvature dipole (BCD) are
symmetry-forbidden. Our calculations reveal
giant, gate-tunable linear and circular dichroism in the terahertz regime, establishing a robust and tunable platform for ultrafast EO modulation in two-dimensional materials beyond the BCD paradigm.
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All authors D. J. P. de Sousa, N. Roldan-Levchenko, C. O. Ascencio, J. D. S. Forte, Paul M. Haney, Tony Low
Strongly Correlated Electrons
Magnetic field-tuned magnetic order and metamagnetic criticality in non-stoichiometric CeAuBi$_2$
Halyna Hodovanets, Hyunsoo Kim, Tristin Metz et al. (+9 more)
We present a detailed study of magnetization, resistivity, heat capacity, and X-ray and
neutron powder diffraction measurements performed on single
crystals of non-stoichiometric CeAuBi$_2$, Au deficiency 18$\%$, a strongly correlated antiferromagnet with Néel temperature T$_N$ = 13.2 K. Field-dependent magnetization measurements reveal a large
magnetic anisotropy at low temperatures with an easy axis along the crystallographic c-axis, in which direction a
spin-flop transition exhibits strong features in magnetization, specific heat, and resistivity at H$_c$ = 75 kOe. The constructed temperature-field phase diagram connects this transition to the suppression of
magnetic order, which evolves from a second-order nature into a first-order transition that bifurcates at the
spin-flop into three transitions below 1 K. The smoothed nature of the metamagnetic transitions in non-stoichiometric CeAuBi$_2$ is well described by an Ising model with weak quenched disorder, suggesting that the presence of Au vacancies is sufficient to smear the complex metamagnetic behavior and tune the critical behavior of
magnetic order.
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All authors Halyna Hodovanets, Hyunsoo Kim, Tristin Metz, Yasuyuki Nakajima, Christopher J. Eckberg, Kefeng Wang, Jie Yong, Shanta R. Saha, David Graf, Nichola P. Butch, Thomas Vojta, Johnpierre Paglione
Strongly Correlated Electrons
Beyond Random Phase Approximation in electron-hole bilayer superfluidity
Filippo Pascucci, Stefania De Palo, Sara Conti et al. (+3 more)
We derive the normal and anomalous proper polarization functions and the screened Coulomb interactions in a two-dimensional superfluid electron-hole
bilayer, including all first-order corrections beyond the Random Phase Approximation (RPA). This requires a modification of the perturbation method as first noted by Nozières and Schrieffer [1, 2]. We discuss the physical origin and magnitude of the first-order corrections in a superfluid system with long-range Coulomb interactions. Unlike conventional superconductivity, Migdal's
theorem does not apply here, so exchange vertex corrections cannot be neglected. The screened electron-electron, hole-hole, and electron-hole interactions in the superfluid state are evaluated as functions of the carrier density. We find that at low density, the strong cancellations between the normal and anomalous components that make screening of the interactions negligible, apply not only within RPA but also with the first-order corrections included. As the density is increased, the normal-anomalous cancellation weakens and screening becomes increasingly significant. We find that the first-order corrections amplify the normal-anomalous difference but only at large momenta exchanged in the two-particle scattering, so their effect on the interactions remains modest. We conclude that the superfluid state RPA is an excellent approximation for the screening and for the effective electron-hole pairing in this superfluid system over the range of densities up to the maximum of the superfluid gap.
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All authors Filippo Pascucci, Stefania De Palo, Sara Conti, David Neilson, Andrea Perali, Gaetano Senatore
Strongly Correlated Electrons · Cross-listed from hep-th
Spontaneous symmetry breaking of $\mathrm{SO}(2N)$ in Gross–Neveu theory from $2+\epsilon$ expansion
Bilal Hawashin and Max Uetrecht
It was recently established that the paradigmatic Gross–Neveu model with $N$ copies of two-dimensional Dirac
fermions features an $\mathrm{SO}(2N)$
symmetry if certain interactions are suppressed. This becomes evident when the theory is rewritten in terms of $2N$ copies of two-dimensional Majorana
fermions. Mean-field theory for the $\mathrm{SO}(2N)$ model predicts, besides the
chiral Ising transition at $g_{c1}$, a second critical point $g_{c2}$ where $\mathrm{SO}(2N)$ is broken down to $\mathrm{SO}(N)\times\mathrm{SO}(N)$. A subsequent Wilsonian renormalization group analysis directly in $d=3$ supports its existence in a generalized theory, where $N_f$ copies of the $4N$-component Majorana
fermions are introduced. This allows to track the
evolution of a (i)
quantum anomalous
Hall Gross–Neveu–Ising, (ii) symmetric-tensor, and (iii) adjoint-nematic fixed point separately. However, it turns out that (ii) and (iii) lose their criticality when approaching $N_f = 1$, suggesting that the transition is first order. In this work, we approach the problem from the lower-critical dimension of two. We construct a Fierz-complete renormalizable Lagrangian, compute the leading order $\beta$ functions,
fermion anomalous dimension, as well as the order parameter anomalous dimensions, and resolve the three universality classes corresponding to (i)–(iii). Before becoming equal to the Gaussian fixed point at $N_f = 1$, (ii) remains critical for all values of $N_f > N_{f,c}^{\mathrm{ST}}(N) \approx 0.56 + 1.48 N +\mathcal{O}(\epsilon)$, which compares well with the estimate of previous studies. We further find that (iii) becomes equal to (i) when approaching $N_f = 1$. An instability is, however, only present in the susceptibility corresponding to the Gross–Neveu–Ising order parameter.
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Strongly Correlated Electrons
Chiral gapped states are universally non-topological
Xiang Li, Ting-Chun Lin, Yahya Alavirad et al. (+1 more)
We propose an operator generalization of the Li-Haldane
conjecture regarding the
entanglement Hamiltonian of a disk in a 2+1D
chiral gapped groundstate. The logic applies to regions with sharp corners, from which we derive several universal properties regarding corner
entanglement. These universal properties follow from a set of locally-checkable conditions on the wavefunction. We also define a quantity $(\mathfrak{c}_{\text{tot}})_{\text{min}}$ that reflects the robustness of corner
entanglement contributions, and show that it provides an obstruction to a gapped boundary. One reward from our analysis is that we can construct a local gapped
Hamiltonian within the same
chiral gapped phase from a given wavefunction; we
conjecture that it is closer to the low-energy renormalization group fixed point than the original parent
Hamiltonian. Our analysis of corner
entanglement reveals the emergence of a universal conformal geometry encoded in the
entanglement structure of bulk regions of
chiral gapped states that is not visible in topological field theory. Our formalism also gives an explanation of the modular commutator formula for the
chiral central charge.
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All authors Xiang Li, Ting-Chun Lin, Yahya Alavirad, John McGreevy
Statistical Mechanics
Group word dynamics from local random matrix Hamiltonians and beyond
Klée Pollock, Jonathan D. Kroth, Jonathon Riddell et al. (+1 more)
We study one dimensional
quantum spin chains whose nearest neighbor interactions are random
matrices that square to one. By employing free probability theory, we establish a mapping from the many-body
quantum dynamics of energy density in the original chain to a single-particle hopping dynamics when the local
Hilbert space dimension is large. The hopping occurs on the Cayley graph of an infinite Coxeter reflection group. Adjacency
matrices on large finite clusters of this Cayley graph can be constructed numerically by leveraging the automatic structure of the group. The density of states and two-point functions of the local energy density are approximately computed and consistent with the physics of a generic local
Hamiltonian: Gaussian density of states and thermalization of energy density. We then ask what happens to the physics if we modify the group on which the hopping dynamics occurs, and
conjecture that adding braid relations into the group leads to integrability. Our results put into contact ideas in free probability theory,
quantum mechanics of
hyperbolic lattices, and the physics of both generic and integrable
Hamiltonian dynamics.
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All authors Klée Pollock, Jonathan D. Kroth, Jonathon Riddell, Thomas Iadecola
Superconductivity
Tailoring Superconductivity with Two-Level Systems
Joshuah T. Heath, Alexander C. Tyner, S. Pamir Alpay et al. (+2 more)
We investigate the impact of two-level systems (TLSs) on superconductivity, treating them as soft modes localised in real space. We show that these defects can either enhance or suppress the superconducting critical temperature, depending on their surface density and average frequency. Using thin-film aluminium as a case study, we quantitatively describe how TLSs modify both the critical temperature and the zero-temperature superconducting gap. Our results thus highlight new opportunities for tailoring material properties through TLS engineering.
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All authors Joshuah T. Heath, Alexander C. Tyner, S. Pamir Alpay, Peter Krogstrup, Alexander V. Balatsky
Statistical Mechanics
Free-Fermion Measurement-Induced Volume- to Area-Law Entanglement Transition in the Presence of Fermion Interactions
Matthew S. Foster, Haoyu Guo, Chao-Ming Jian et al. (+1 more)
At a generic volume- to area-law
entanglement transition in a many-body system,
quantum chaos is arrested. We argue that this tends to imply the vanishing of a certain "mass" term in the field theory of the measurement-induced phase transition (MIPT) for monitored, interacting
fermions. To explore this idea, we consider the MIPT with no conserved quantities that describes 1D monitored, interacting Majorana
fermions in class DIII. This is the most general problem of interacting
fermions with weak
fermion parity measurements. Without interactions, it is known that a noninteracting MIPT separates the area-law phase from a log-enhanced "thermal metal" phase at sufficiently weak monitoring. We
conjecture that the MIPT with interactions is the same as the noninteracting one in this case; the volume-law phase arises through the dangerously irrelevant mass. The physical picture is that the mass represents a local
Fermi's golden rule interparticle scattering rate density that is tantamount to the entangling rate density. The latter must vanish continuously at a continuous MIPT. On the other hand, the field theory capturing the MIPT for monitored
fermions with additional continuous
symmetries is expected to be different, because the interactions introduce additional terms associated to conserved Noether currents. We propose numerical tests of our
conjecture. In addition, we analytically identify a candidate noninteracting critical point representing the MIPT, using a controlled $\epsilon$-expansion.
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All authors Matthew S. Foster, Haoyu Guo, Chao-Ming Jian, Andreas W. W. Ludwig
Strongly Correlated Electrons
Exact nematic and mixed magnetic phases driven by competing orders on the pyrochlore lattice
Niccolò Francini, Lukas Schmidt, Lukas Janssen et al. (+1 more)
Pyrochlore magnets are a paradigmatic example of three-dimensional frustrated systems and provide an excellent platform for studying a variety of exotic many-body phenomena, including
spin liquids, nematic phases, fragmentation, and order by disorder. In recent years, increasing
attention has been devoted to bilinear
spin models on this
lattice, where multiple
magnetic phases can be degenerate in energy, often stabilizing unconventional
magnetic states. In this work, we focus on one such model, parametrized by the interaction coupling $J_{z\pm}$, which defines a line in parameter space corresponding to the phase boundary between three distinct
magnetic phases. Using a combination of analytical and numerical methods, we show that this model exhibits an order-by-disorder mechanism at low temperatures, giving rise to a mixed
magnetic phase. This realizes a $\mathbf q=0$ long-range-ordered phase in a pyrochlore magnet characterized by two distinct order parameters, which we denote as the $A_2 \oplus \psi_2$ phase. Furthermore, at $J_{z\pm} = 1/\sqrt{2}$, the model acquires a subextensive number of discrete
symmetries, which preclude the stabilization of conventional long-range order and instead lead to the emergence of a novel nematic phase. We characterize this nematic phase, describe how its ground-state configurations are constructed, and analyze its stability at higher temperatures and under small deviations from $J_{z\pm} = 1/\sqrt{2}$.
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All authors Niccolò Francini, Lukas Schmidt, Lukas Janssen, Daniel Lozano-Gómez