Mesoscale and Nanoscale Physics
Tunable flat bands and their signatures in electronic specific heat of an Aharonov-Bohm triangular quantum network
Sanchita Nandi and Santanu K. Maiti
Quantum networks composed of loop-like structures provide a rich platform for exploring electronic transport phenomena and have been widely studied in various contexts. However, their thermal response remains relatively unexplored, motivating us to investigate it in the present work. We consider a tight-binding (TB)
quantum network composed of a finite number of triangular plaquettes, where neighboring plaquettes are connected through single bonds and each triangular loop is threaded by an Aharonov-Bohm (AB) flux $\phi$. The interplay of nonuniform site coordination, hopping asymmetry, and
quantum interference gives rise to both dispersive and completely flat energy levels. We derive an analytical condition involving the TB parameters under which one of the energy branches becomes independent of the electronic momentum. We further show that the AB flux $\phi$ provides a direct means of tuning the position of the flat band. The characteristic features of the energy spectrum associated with this
quantum geometry are reflected in the thermal response, which we investigate through the electronic specific heat (ESH). In particular, we demonstrate that the position of the flat band manifests itself as a distinct feature in the ESH, establishing a direct connection between the flat-band formation and the thermal response of the system. Thus, the ESH provides an alternative route for identifying the presence of a flat band, consistent with the analytical condition and the corresponding energy dispersion. Moreover, the AB flux allows the ESH to be selectively regulated through the tuning of the flat-band position. The proposed approach provides a simple complementary means of identifying momentum-independent energy levels and may be extended to other simple and complex
quantum networks supporting flat bands.
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Mesoscale and Nanoscale Physics
Engineering nonlinear spin-orbit torque driven by intra-band transport in MoSe$_2$/CrI$_3$ and WSe$_2$/CrI$_3$ van der Waals heterostructures
Leyla Majidi, Azadeh Faridi and Reza Asgari
The role of nonlinear carrier dynamics in current-driven
spin phenomena remains poorly understood in van der Waals
magnetic heterostructures. Here, we investigate the
spin polarization and the resulting
spin-orbit torque (SOT) in transition-metal dichalcogenide/chromium iodide (TMDC/CrI$_3$)
heterostructures, focusing on WSe$_2$/CrI$_3$ and MoSe$_2$/CrI$_3$, in the zero-Rashba
spin-orbit coupling (SOC) limit and beyond the linear-response regime. We find that linear
spin polarization is forbidden by
symmetry, making nonlinear intraband transitions the dominant mechanism in this regime. Consequently, the current-driven
spin response differs fundamentally from conventional linear-response predictions. The resulting nonlinear
spin polarization generates a purely field-like torque whose magnitude and sign depend sensitively on the chemical potential and doping type, with pronounced asymmetries between n- and p-doped systems. A strong material dependence is also observed: n-doped MoSe$_2$/CrI$_3$ exhibits a torque nearly an order of magnitude larger than that of WSe$_2$/CrI$_3$, together with two sign reversals, reflecting differences in their SOC and proximity-exchange parameters. Structural and electrostatic control through the twist angle and gate electric field provides additional means of tuning the nonlinear torque, including substantial modulation and controllable sign reversals. These findings establish TMDC/CrI$_3$ bilayers as a versatile platform for engineering nonlinear
spin-orbit phenomena in ultrathin, low-power spintronic devices.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.str-el
Cooper pair charge Kondo effect in a hybrid quantum dot - superconductor device
Luca Gonfiantini, Lorenzo Maffi and Michele Burrello
We consider a tunable hybrid device composed of four
quantum dots and a floating superconducting island – the so-called poor man's tetron – close to its effective particle-hole symmetric point and coupled to four external leads. We predict the onset of a charge Kondo effect mediated by Cooper pairs, resulting from the strong crossed Andreev reflections that dominate its low-energy behavior. This two-channel Kondo effect makes the poor man's tetron behave as a double Cooper pair splitter, turning uncorrelated incoming electrons into spatially separated Cooper pairs. Based on renormalization group techniques, we analyze both its weak and strong coupling regimes and we determine its non-Fermi
liquid signatures. Our estimates indicate that the fractional conductance and transport features associated to this two-channel charge Kondo effect can be observed over a broad range of temperatures and anisotropies in realistic experimental conditions.
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Mesoscale and Nanoscale Physics
Anyonic molecules through the trion looking glass
Hao-Ran Cui, Vladimir Calvera, Umang Mehta et al. (+1 more)
Motivated by recent optical measurements in twisted MoTe$_2$ homobilayers, we numerically study the binding of itinerant anyons to ordinary electronic bound states. Using a minimal few-body model of an anyon alongside holes and electrons in a Gaussian trapping potential, we show that a fractionally charged bound state comprised of an anyon and an ordinary electronic trion can become favorable nearby local electrostatic defects. The resulting object is an anyonic molecule wherein the anyon is bound to the trion “
nucleus,” which in turn is localized to the defect and can be excited optically. We find that the resulting anyon-trion can exhibit a photoluminescence red-shift relative to the ordinary trapped trion, with binding on the meV scale for parameters relevant to twisted MoTe$_2$. We find that the value of this red-shift depends on $\textit{both}$ the anyon's fractional charge and its kinetic energy, thereby encoding both universal and non-universal anyon properties. Our results are qualitatively consistent with observations in twisted MoTe$_2$.
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All authors Hao-Ran Cui, Vladimir Calvera, Umang Mehta, Hart Goldman
Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.dis-nn
Non-vanishing Density of States in Disordered Weyl Semimetals
Justin H. Wilson
There is disagreement in the literature concerning whether the nodal point of a three-dimensional Weyl semimetal survives weak short-range disorder: instanton calculations including fluctuations claim that the zero-energy density of states $\rho(0)$ vanishes, while exact numerics find a systematically finite number. We settle this disagreement with a full saddle-point calculation, including both instanton and fluctuations. Within the supersymmetric formulation for disorder, the instanton obeys a nonlinear Weyl equation whose solution is an exact $j=1/2$ hedgehog whose full functional form we numerically compute. We then compute the fluctuations about this saddle point, carefully identifying all zero modes, and computing the reduced superdeterminant as a convergent Fredholm determinant. No fermionic zero mode beyond a Kramers doublet exists, and at finite disorder $w$, the fluctuations become a finite one-loop prefactor, $\rho(0)=\mathcal{A} w^{-4} \exp(-s^*/w^2)(1+O(w^2))$, in normalized units with $s^* = 6.4163(2)$ and $\mathcal{A} = 27.47(8)$ for Gaussian-correlated disorder. This expression matches exact numerics on a single Weyl cone over four orders of magnitude with no fitted parameters (the amplitude is $\times 0.76$ the one-loop value), establishing that the density of states is finite for any disorder strength.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.dis-nn
Upper critical dimension for dirty Weyl semimetal-to-metal quantum phase transitions
Yongtai Li and Bitan Roy
Weyl or Dirac
fermions with the iconic linear energy-momentum relation and average density of states (ADOS) $\rho(E) \sim |E|^{d-1}$ at energy $E$ in $d$ spatial dimensions, constitute a unique setup to study the disorder-driven semimetal-to-metal
quantum phase transition (QPT) between ballistic (realized for weak disorder) and diffusive (stabilized at stronger disorder) quasiparticles. Such a QPT takes place only for $d>2$ and falls beyond the realm of the Anderson metal-to-
insulator transition. From numerically computed ADOS (using the kernel
polynomial method) in dirty Weyl systems in $d=2$ to $6$, here we show that $d=2$ and $d=4$ are the lower ($d_\ell$) and upper ($d_u$) critical dimensions for such an unconventional QPT, respectively, as suggested from the solution of quasiparticle lifetime within the self-consistent Born approximation. Consequently, for $d \geq 4$ the associated correlation length exponent is found to be $\nu \approx 0.5$ (within numerical accuracy). However, the dynamic scaling exponent at the
quantum critical point is pinned close to $z \approx d/2$ (numerically) for any $d \geq 3$, which is shown to be an exact result from a field-theoretic renormalization group calculation. Therefore, Weyl semimetal-to-metal QPTs can be studied field theoretically around both $d_\ell$ and $d_u$.
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Mesoscale and Nanoscale Physics
Projected amorphous topological insulators
Archisman Panigrahi and Bitan Roy
We introduce projected amorphous topological
insulators (PATIs) that despite containing only a fraction ($x$) of otherwise randomly selected disconnected sites of a parent
crystal, feature a quantized global topological invariant (strong PATIs) when its effective
Hamiltonian is constructed by integrating out the residual sites of the original
lattice. Within the topological regime of the parent model, additionally, there exists a critical $x$ below which such systems foster a fragile PATI that only supports quantized local topological marker on a small fraction of sites therein. Both strong and fragile PATIs accommodate in-gap modes near the boundary. The system also hosts a normal
insulator in the entire trivial parameter regime of the
lattice-based model for any $x$, devoid of gapless boundary modes, for which both global topological invariant and local topological marker vanish. We demonstrate these possibly generic outcomes by starting with a parent square
lattice-based model for time-reversal
symmetry breaking
insulators. Then the strong-to-fragile PATI
quantum phase transition, tunable via $x$, is characterized by the mean correlation length exponent $\nu \in (1.00,1.46)$.
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Mesoscale and Nanoscale Physics
Incipient superconductivity and tunable Chern insulators in twisted bilayer-trilayer graphene
Derek Waleffe, Aryana Bhattacharyya, Manish Kumar et al. (+7 more)
Moiré superlattices assembled by twisting Bernal and rhombohedral multilayer
graphene host a rich set of interaction-driven
magnetic and topological states, yet superconductivity has not been observed in these systems except in proximity to a transition-metal dichalcogenide. Here we report incipient superconductivity and tunable Chern
insulators in twisted bilayer-trilayer
graphene encapsulated by hexagonal boron nitride. Across twist angles from $\theta = 1.05^\circ$ to $1.50^\circ$, Chern
insulators form at integer and fractional moiré fillings for electron doping, with Chern numbers up to |C| = 3 set by twist angle and tuned by doping. At $\theta = 1.18^\circ$, a
symmetry-broken metallic region forms for hole doping and hosts a trivial
insulator at band filling $\nu = -2$. Displacement field alone drives this
insulator into a pocket of incipient superconductivity with a sharp transition, a well-defined critical current, and a critical temperature that peaks near the insulating boundary, although the resistance does not fall to zero. In-plane
magnetic field expands the pocket, which persists to more than four times the weak-coupling Pauli limit, and stabilizes a second pocket in which Fraunhofer-like modulation of the critical current signals phase-coherent pairing. Twisted bilayer-trilayer
graphene thus offers a single gate-tunable system in which pairing can be interfaced with Chern
insulators whose
topology is itself an adjustable parameter.
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All authors Derek Waleffe, Aryana Bhattacharyya, Manish Kumar, Eric Maginnis, Anna Okounkova, Tobias Faehndrich, Kenji Watanabe, Takashi Taniguchi, Joshua Folk, Matthew Yankowitz
Mesoscale and Nanoscale Physics
Pomeranchuk-like electronic localization above 100 K in twisted MoS$_{2}$
Zhiren Xiong, Jianqi Huang, Ruyue Han et al. (+8 more)
Twisted transition-metal dichalcogenides (TMDs) have manifested a rich variety of emerging physical phenomena, yet experimental studies have so far been largely limited in their valence bands (p-doped). Here, we show correlated electronic states in the conduction bands (n-doped) of near-AA-twisted bilayer MoS$_2$ with twist angles ranging from $\sim2.3^\circ$ to $\sim3.5^\circ$, down to the mK temperature regime. A strongly reconstructed correlated phase diagram as a function of twist-angle has been observed - correlated gaps persist to temperatures approaching $160$ K at small twist angles, but collapse to only $\sim20$ K at intermediate angles, where a richer landscape of interaction-driven states emerges. At the largest twist-angle $\sim 3.5\,^{\circ}$, correlated resistance at 1 electron per moiré unit
cell is enhanced upon heating, consistent with thermally assisted localization, or, a Pomeranchuk-like behaviour. Its
magnetic-field response, however, is highly anisotropic, which differs markedly from that of canonical isospin moiré Pomeranchuk effect in
graphene systems. Strikingly, such signature can persist even above 100 K around a filling of 2 electrons per moiré, despite of its weak resistive nature. Our results establish the twisted MoS$_2$ as a platform for studying the complexity of charge localization, internal flavour degrees of freedom, and band
topology in conduction bands of semiconducting moiré systems.
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All authors Zhiren Xiong, Jianqi Huang, Ruyue Han, Hanwen Wang, Hui Ding, Jianming Lu, Jianpeng Liu, Zheng Vitto Han, Xingdan Sun, Siwen Zhao, Baojuan Dong
Mesoscale and Nanoscale Physics · Cross-listed from physics.app-ph
Topological-Insulator Heterophase Gate Stacks for Transistor Electrostatics
Minuk Song, Jiwan Kim, MD Gius Uddin et al. (+25 more)
Conventional gate-stack scaling reduces dielectric thickness and increases permittivity while largely treating the position and electronic character of the gate-side screening boundary as fixed. Here we show that this boundary can be engineered by converting the surface of the topological
insulator Bi\textsubscript{2}Se\textsubscript{3} into insulating high-$\kappa$ BiF\textsubscript{3}. Position-resolved calculations reveal a gap-opened immediate amorphous-BiF\textsubscript{3}/crystalline-Bi\textsubscript{2}Se\textsubscript{3} interface and a reconstructed gap-closed Bi\textsubscript{2}Se\textsubscript{3}-derived state in the adjacent subinterface layer, accompanied by a localized interfacial dipole. Capacitor measurements independently resolve a finite series response consistent with electronic compressibility at this boundary; this response lowers the nominal stack capacitance. Despite this capacitance penalty, MoS\textsubscript{2} transistors with closely matched BiF\textsubscript{3} thicknesses and a common BiF\textsubscript{3}/MoS\textsubscript{2} channel-side material interface exhibit near-thermionic-limit switching, negligible hysteresis and substantially weaker subthreshold drain-bias dependence than BiF\textsubscript{3}-only controls. These results identify the position and electronic character of the gate-side screening boundary as additional design variables for transistor electrostatics beyond nominal dielectric capacitance.
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All authors Minuk Song, Jiwan Kim, MD Gius Uddin, Wonseok Kim, Jihun Park, Han Uk Lee, Dong Won Jeon, Dohyung Lee, Lide Yao, Jouko Lahtinen, Gyunghyun Jang, Soohyun Min, Yonas Tsegaye Megra, Xiaoqi Cui, Seungwoo Choi, Yunyun Dai, Sang Hoon Chae, Keun Su Kim, Dong-Ho Kang, Hyeon-Jin Shin, Wooseok Song, Seth Ariel Tongay, Chul-Ho Lee, Manish Chhowalla, Sung Beom Cho, Zhipei Sun, Kibog Park, Hoon Hahn Yoon
Mesoscale and Nanoscale Physics
Real-axis least-squares bath discretization for real-time transport in quantum-dot Josephson junctions
Ruixin Zhou, Bing Dong and Yiyan Wang
Efficient real-time methods are essential for resolving transient coherence and nonlinear transport in driven superconducting nanostructures. Such simulations remain challenging because finite representations of the BCS continuum generate recurrences, while the damping used to suppress them smears gap-edge structure and artificially shortens coherent lifetimes; finite-broadening regularization of the gap-edge singularity likewise imposes a lifetime-resolution floor. Here we extend the driven Liouville–von Neumann approach to superconducting reservoirs—a noninteracting
quantum dot with Bogoliubov–de Gennes leads—building an explicit-
Hamiltonian framework that hosts a family of bath discretizations (uniform and Gaussian baselines and a new real-axis least-squares recipe, with mode energies, spectral weights, and mode-resolved dampings optimized jointly under gap-aware constraints)—making the broadening an independently calibrated numerical parameter whose leading long-time effect extrapolates controllably along the joint ($\gamma\to0$, $N_b\to\infty$) refinement path while cutting computational cost by over an order of magnitude versus the high-resolution DLvN reference. The compressed baths recover established current-phase relations, multiple-Andreev-reflection structure, quasiparticle-trapping oscillations, and integer and fractional Shapiro locking; the lifetime analysis yields the parameter-free leading-order relation $\kappa\simeq w_{\mathrm{bath}}\gamma_{\mathrm{eff}}$ and resolves damping-induced decay rates below the resolution scale of a previous finite-broadening calculation. As an explicit
Hamiltonian reservoir representation, the framework generalizes naturally to multiterminal normal–superconducting geometries and offers a route toward interacting impurity solvers, while finite-gap strong-drive locking amplitudes mark its present quantitative boundary.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci
Subnanometer thermodynamic overlayers on bimetallic nanoparticles
Caitlin A. McCandler, Xianzhuo Lao, Jie Liu et al. (+3 more)
Nanoparticle properties are governed by their surfaces, yet their atomic-scale surface structures remain challenging to predict. Here, we report that bimetallic nanoparticles can form a thermodynamically controlled "shell-dimer" architecture in which one metal forms an overlayer only a few atomic layers thick on another. Using Au-Rh as a model system, atomic-resolution imaging and molecular dynamics show that an ultrathin Au overlayer forms on Rh, stabilized by competition among surface, interfacial, and strain energies. Anisotropic strain limits its growth to the subnanometer scale, and changes in surface chemistry can destabilize the overlayer altogether. Across a range of bimetallic nanoparticles, we found that overlayer formation is associated with elemental immiscibility and
lattice mismatch. These findings provide a basis for understanding and controlling surface structures in multimetallic nanoparticles.
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All authors Caitlin A. McCandler, Xianzhuo Lao, Jie Liu, Huipu Liu, Kristin A. Persson, Peng-Cheng Chen
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Avoided crossings in spin-boson systems: consequences for adiabatic state preparation
Joona Marjamäki, Robert van Leeuwen and Riku Tuovinen
Avoided crossings in the correlated many-body spectrum play a central role in determining the conditions for adiabatic state preparation in interacting
quantum systems. We investigate this connection in finite
spin-
boson systems by combining exact diagonalization of the many-body spectrum with time-dependent simulations of adiabatic switching protocols. By comparing the adiabatically prepared state with the exact ground state, we determine the switching times required for reliable preparation as a function of the
spin-
boson coupling strength and bosonic mode structure. We show that regions of small many-body level spacings, associated with avoided crossings, impose the strongest constraints on adiabatic preparation and explain the observed dependence of the required switching times on the interaction strength. Furthermore, while the ground-state energy follows the overall spectral trends, local observables such as Pauli
matrix expectation values exhibit additional non-monotonic behavior arising from coherent oscillations in finite systems. These findings can provide concrete
benchmarks for both the theoretical treatment of open
quantum systems and practical implementations in
quantum simulation and
qubit control.
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Mesoscale and Nanoscale Physics
Spin-Polarized Magnetic Metal Electrodes for Magnetic Tunnel Junctions
Zhiyuan Duan, Peixin Qin, Li Liu et al. (+7 more)
Magnetic tunnel junctions are foundational components of spintronic
memory, sensing, and computing, and their performance depends critically on the
magnetic metallic electrodes. This Perspective examines electrode materials through the lens of
magnetic order and the distinct microscopic mechanisms that generate
spin-selective tunneling. Conventional ferromagnets, including CoFeB and half-metallic Heusler
alloys, support exchange-split electronic states and
symmetry-filtered tunneling, whereas compensated collinear and noncollinear antiferromagnets exploit sublattice selectivity,
spin-orbit anisotropy, vector
spin textures, and
magnetic multipoles. Altermagnets provide a collinear, zero-net-moment route based on
symmetry-allowed momentum-dependent
spin splitting. Across these material classes, we compare the origins of tunneling polarization, the roles of barrier evanescent states and interface termination, and strategies for electrically writing and reading the relevant
magnetic order. This comparison reveals a broader design principle: effective electrode polarization is not a scalar bulk quantity, but a momentum-, orbital-,
symmetry-, and interface-resolved transport property. Beyond the pursuit of ever larger tunneling magnetoresistance, future progress will depend on converting the unconventional
spin polarization of emerging
magnetic metals into electrically addressable, thermally robust, and reproducible tunneling functionality at realistic interfaces.
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All authors Zhiyuan Duan, Peixin Qin, Li Liu, Guojian Zhao, Sixu Jiang, Xiaoyang Tan, Jingyu Li, Xiaoning Wang, Ziang Meng, Zhiqi Liu
Mesoscale and Nanoscale Physics
Cavity-waveguide coupling in phononic crystals
Jakub Rosiński, Benjamin Mayer, Hubert J. Krenner et al. (+1 more)
Phononic
crystal platforms provide a promising route toward scalable on-chip
quantum networks, where mechanical excitations mediate interactions between solid-state
qubits. A key building block of such architectures is the cavity-waveguide system, in which localized mechanical modes couple to propagating phononic modes. However, a quantitative understanding of the mechanisms governing this coupling remains incomplete. In this work, we investigate the interaction between localized modes of snowflake-type phononic
crystal cavities and a phononic
crystal waveguide using finite-element simulations and experimental measurements. We show that the coupling strength is primarily governed by the spatial overlap between the displacement fields of the corresponding isolated cavity and waveguide modes. After accounting for the effective-mass dependence of the normalized cavity displacement amplitude, we establish a strong correlation between the spatial overlap and the interaction strength across a wide range of mode combinations. Deviations from this leading-order behavior are associated with Bloch-phase effects, variations in waveguide group velocity, and intrinsic hybridization of waveguide modes. Furthermore, we provide experimental evidence for cavity-waveguide coupling in a GaAs phononic
crystal membrane by observing a clear resonance in the spectral broadening of the photoluminescence emission from an embedded
quantum dot, which serves as a local probe of the mechanical field. The observed resonance at approximately 398 MHz is in good agreement with the corresponding cavity resonance near 395 MHz predicted by finite-element simulations. Our results identify spatial mode overlap as a leading-order design parameter for cavity-waveguide coupling and provide practical guidelines for controlling interactions between localized and propagating modes in phononic
crystal structures.
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All authors Jakub Rosiński, Benjamin Mayer, Hubert J. Krenner, Paweł Machnikowski
Mesoscale and Nanoscale Physics
Nodal-Line Semimetals with Non-Quantized Berry Phase
Zhi-Xia Li, Liangliang Huang, Min-Xue Yang et al. (+3 more)
Nodal-line semimetals (NLSMs) are topological materials characterized by one-dimensional band crossings in momentum space, which typically carry a Berry phase quantized to integer multiples of $\pi$. Here, we extend the conventional paradigm to a class of NLSMs in which the Berry phase can take arbitrary fractional or even irrational multiples of $\pi$. This non-quantized Berry phase leads to a splitting of Landau levels when a
magnetic field is applied parallel to the nodal ring, an effect that can be detected via Shubnikov-de Haas oscillations in the magnetoconductivity. Despite the absence of a quantized topological invariant, drumhead-like surface states with weak dispersion persist at open boundaries. Notably, two identical surface states localize on the same boundary, in contrast to conventional NLSMs, where they reside on opposite boundaries. A systematic
symmetry analysis shows that such NLSMs can be realized in a broad range of
magnetic space groups. Our work opens a new avenue for exploring NLSMs beyond the conventional framework of a quantized Berry phase.
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All authors Zhi-Xia Li, Liangliang Huang, Min-Xue Yang, Feng Tang, D. Y. Xing, Wei Chen
Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci
Selective strain tuning of nonequilibrium multiferroic dynamics in BiFeO$_\text3$
Chenhang Xu, Patrick Liu, Bo Zhang et al. (+11 more)
Quantum materials are characterized by intertwined orders, and a fundamental goal in condensed matter physics is to achieve their selective control in such a way that one order parameter can be tuned while leaving others largely unaffected. Although significant progress has been made in thermal
equilibrium, realizing such control out of
equilibrium remains highly challenging. Here we employed in-situ tensile strain to selectively manipulate the photoinduced
lattice dynamics associated with ferroelectric and
magnetic orders in multiferroic BiFeO$_3$. By applying MeV ultrafast electron diffraction to freestanding BiFeO$_3$ membranes under tunable strain, we showed that tensile strain markedly suppresses the ultrafast photoinduced reduction of the ferroelectric displacement. By contrast, the photoinduced dynamics of the antiferrodistortive rotation of the oxygen octahedra, which modulates the
magnetic order, remains insensitive to strain. Not only do these findings reveal distinct microscopic pathways underlying nonequilibrium multiferroic dynamics, they also establish tunable strain as an effective route for engineering ultrafast phase control in correlated materials.
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All authors Chenhang Xu, Patrick Liu, Bo Zhang, Minyong Han, Henry G. Bell, Cameron J. R. Duncan, Yusong Liu, Patrick L. Kramer, Randy Lemons, Jake D. Koralek, Alexander H. Reid, Dong Qian, Harold Y. Hwang, Alfred Zong
Mesoscale and Nanoscale Physics
Library of carbon nanotube junctions: data-driven insights into structure-magnetotransport relationships
Juan Alberto Canché-Martín, Teresa Kulka, Jacek A. Majewski et al. (+3 more)
Electronic transport in carbon nanotube (CNT) assemblies is controlled by a heterogeneous population of CNT–CNT junctions, yet most microscopic studies consider only a few representative systems. Here, we construct a library of 146 single-walled carbon nanotube (SWCNT)–SWCNT junctions spanning broad structural and electronic diversity and analyse their magnetotransport using an automated workflow combining molecular dynamics, tight-binding theory, Peierls
magnetic coupling, and non-
equilibrium Green's functions.The resulting transport data are subsequently analysed using machine-learning methods. Two complementary transport descriptors reveal distinct structure–transport hierarchies. The averaged first transmission-step value is governed primarily by the mean chiral angle of the two nanotubes forming a junction, whereas the energy gap of the junction depends predominantly on the metallic or semiconducting character of the constituent CNTs. Temperature generally suppresses the averaged transmission while reducing the extracted gap, whereas a perpendicular
magnetic field affects transmission much more strongly than the gap. Signatures of interference-driven transport remain visible even at $300~\mathrm{K}$. Notably, semiconducting–semiconducting junctions retain the largest gaps but, once shifted into their conducting regime, can exhibit transmission comparable to or exceeding that of metallic junctions. These results establish statistically robust junction-level trends that can inform future network-scale models of CNT assemblies.
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All authors Juan Alberto Canché-Martín, Teresa Kulka, Jacek A. Majewski, Irina V. Lebedeva, Maciej Marchwiany, Karolina Z. Milowska
Mesoscale and Nanoscale Physics
Quantum heat transport and effects of quantum thermal devices in noncommuting coupled spins
Yitian Chen, Junran Kong, Huan Liu et al. (+1 more)
Quantum heat transport governs energy exchange processes and statistical laws in non-
equilibrium quantum systems, and plays a pivotal role in
quantum thermodynamics. We investigate the steady-state thermal transport of a noncommuting coupled
spin system. We employ the
quantum dressed master equation approach within the framework of open
quantum system theory to accurately analyze the non-
equilibrium dynamics, ensuring the validity of transport results in the strong coupling regime. Our results demonstrate that noncommuting
spin coupling serves as a significant resource for modulating the nonlinearity of the heat current. Specifically, in the weak
spin-coupling regime, the system exhibits robust negative differential thermal conductance (NDTC) across various
spin numbers. By deriving analytical expressions for the heat current in both the single-
spin and large-
spin limits, we reveal that this NDTC behavior is governed by microscopic cycle fluxes. Physically, this arises because
spin excitation channels induced by the cold reservoir are suppressed under a large temperature bias, thereby blocking energy exchange cycles. Conversely, in the strong
spin-coupling and large temperature bias regime, the
quantum system demonstrates pronounced thermal rectification. This high rectification efficiency originates from the unidirectional saturation of the heat current, rendering the system a promising candidate for high-performance thermal diodes. Furthermore, we extend the model to a three-terminal configuration to construct a
quantum thermal transistor. By manipulating the temperature of the gate reservoir, we achieve efficient modulation and amplification of heat flow between the source and drain. The heat amplification factor is shown to far exceed unity in specific operating regions, confirming significant thermal amplification.
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All authors Yitian Chen, Junran Kong, Huan Liu, Chen Wang
Mesoscale and Nanoscale Physics
Valley Berry curvature dipole induced nonlinear valley Hall effect
Lulu Xiong, Xue-Jin Zhang, Zeying Zhang et al. (+4 more)
Valley Hall effect is a signature effect in the field of valleytronics, and recent studies have pushed this effect into the nonlinear regime. Here, we reveal a previously unexplored type of nonlinear valley Hall effect which arises from a valley Berry
curvature dipole (vBCD) mechanism. We show this nonlinear valley Hall effect is forbidden for conventional time-reversal-connected valleys, but is supported in the class of valleytronic systems featuring time-reversal-invariant valleys. The candidate layer groups and detailed
symmetry constraints on vBCD are obtained. It shows the nonlinear valley Hall response, as well as the nonlinear charge Hall response, can be well controlled by tuning the driving field direction. We demonstrate our proposal in an effective model study and in a concrete material example, strained Nb$_{3}$SBr$_{7}$, by first-principles calculations. The nonlocal transport signature of this vBCD induced nonlinear valley Hall effect is also discussed.
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All authors Lulu Xiong, Xue-Jin Zhang, Zeying Zhang, Yinning Zhou, Jin Cao, Cong Xiao, Shengyuan A. Yang
Mesoscale and Nanoscale Physics
Antisymmetric breathing in altermagnetic skyrmions
Yunxi Jiang, Chen Xuan, Xi Chen et al. (+3 more)
A skyrmion in an altermagnet with \(d\) wave
symmetry consists of two elliptical sublattice textures with perpendicular long axes. For each sublattice component $\eta=A,B$, we define an effective skyrmion radius $R_\eta=\sqrt{a_\eta b_\eta}$, where $a_\eta$ and $b_\eta$ are the distances from the skyrmion center to its boundary along $y$ and $x$, respectively. For the anisotropic exchange parameters studied, the
equilibrium radius at zero field is smaller than in a reference with parallel sublattice textures and otherwise identical parameters. A
magnetic field perpendicular to the film expands one sublattice skyrmion and contracts the other, generating a radius difference $\dR=R_A-R_B$ and a net
magnetic moment. The exchange modulation used to represent uniaxial strain also produces a nonzero radius difference at zero field. Because the strong and weak exchange directions are interchanged between the two sublattices, a common directional change of the exchange couplings increases one radius and decreases the other. Unlike the
magnetic coupling, this mechanism vanishes when the two sublattice exchange tensors become identical. The radius difference also supports an antisymmetric breathing mode. After a short field pulse, it oscillates in quadrature with the uniform helicity, the common rotation of the wall magnetization within the film plane, at \(49.5\,\mathrm{GHz}\) for the reference parameters.
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All authors Yunxi Jiang, Chen Xuan, Xi Chen, Zhikai Wang, Qinfeng Zhu, Hao Yu
Mesoscale and Nanoscale Physics
Light-induced rectified orbital magnetization in electron-hole bilayers
Erlend Syljuåsen, Gabriel Cardoso, Esra Ilke Albar et al. (+3 more)
Circularly polarized light can rectify orbital motion into a static magnetization through the inverse Faraday effect (IFE), but in electron-hole bilayers the electron and hole contributions cancel exactly when their properties are equivalent. We show that electron-hole bilayers in transition-metal dichalcogenide platforms avoid this cancellation through effective-mass asymmetry alone, and that the surviving orbital IFE is sensitive to interlayer coupling. In the weak-coupling regime, a two-component Drude description yields an induced magnetization of order one Bohr magneton per carrier for representative terahertz driving. In the strong-coupling regime, where the carriers bind into interlayer
excitons, we treat the relative motion using a hydrogenic model with a Rytova-Keldysh interaction and obtain a reduced but finite response. We give closed-form expressions that allow estimates across a broad parameter range and identify where the response is largest.
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All authors Erlend Syljuåsen, Gabriel Cardoso, Esra Ilke Albar, Patrick J. Wong, Angel Rubio, Alexander V. Balatsky
Mesoscale and Nanoscale Physics
Nonequilibrium Dirac condensate in bosonic Kitaev chain
Kazuki Yamamoto and Youichi Yanase
We explore a nonequilibrium Bose-Einstein condensate (BEC) in a bosonic Kitaev chain. Within a mean-field framework, we show that bosonic superfluid order develops once the pairing strength exceeds a critical threshold. The condensate order parameter adopts an alternating phase between even and odd sites, giving rise to a spontaneous sublattice ordering. By mapping the emergent sublattice degrees of freedom onto a pseudospin, the elementary Bogoliubov excitation is described by a non-Hermitian Dirac
Hamiltonian, displaying two prominent features: a re-entrant bosonic Andreev bound state localized around boundaries, and a macroscopic degeneracy of exceptional Majorana
bosons at the critical point.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.dis-nn
Perfect resonance and fragile localization suppression in correlated disordered chains
Zhixuan Zhao and Jun Li
Spatial correlations can suppress scattering in disordered chains and produce perfectly transmitting resonances. The practical value of this protection, however, depends not on the resonance peak itself but on the width of the surrounding transmission window and its sensitivity to local ordering errors. We show that a resonance can remain exactly transparent at its center while arbitrarily rare adjacent-swap errors restore an inverse localization length proportional to the square of the energy detuning. For lossless single-channel chains assembled from independent blocks of fixed length and composition, this positive quadratic term is guaranteed by a local scattering invariant and holds for every arrangement and every fixed swap probability between zero and one. With exact tuning and matched contacts, the central transmission remains unity. A microscopic
quantum chain exhibits both higher-order suppression of scattering in the ideal recursive arrangement and the predicted response to local exchanges. These results reveal a limitation of spatial ordering that is invisible to a measurement at the resonance alone: spatial ordering protects the resonance peak, not the transport around it. The effect can therefore be tested experimentally by measuring transmission spectra before and after exchanges, without identifying microscopic defects.
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Mesoscale and Nanoscale Physics
Zhi-Hai Liu, Jiang Zhang, Guilu Long et al. (+1 more)
Spin is typically traced out in the description of
quantum-dot-based Kitaev chains to simplify the construction of Majorana
fermions. Yet the intrinsic
spin structure of poor-man's Majorana modes in minimal Kitaev chains under finite Zeeman fields offers a natural interface for the Kitaev parity
qubit to interact with other spinful systems. Here, we establish such a platform to bridge the parity
qubit and a
quantum-dot
spin qubit, with the effective coupling governed by the
spin-dependent delocalization of the Majorana modes. Depending on whether the
spin qubit is coupled to one or two chains constituting the parity
qubit, the parity-
spin coupling exhibits distinct forms: an anisotropic parity-conserving exchange interaction or a nontrivial exchange tensor tunable via the interchain superconducting-phase bias. Leveraging fast
spin-
qubit manipulation, we further demonstrate universal parity-
qubit control, high-fidelity
qubit-state readout, and entangling operations between the parity and
spin qubits. These results turn the spinful structure of poor-man's Majoranas from a finite-field imperfection into a resource for hybrid
quantum control.
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All authors Zhi-Hai Liu, Jiang Zhang, Guilu Long, H. Q. Xu
Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.quant-gas
Moiré droplet of ultracold Bose gases in a twisted-bilayer optical lattice
Tianqi Luo, Jing Zhang and Xiaoling Cui
We report the emergence of Moiré droplet in two-dimensional ultracold
bosons subjected to a
spin-dependent optical
lattice, effctively realizing a twisted-bilayer configuration. We show that the droplet formation dramatically enhances the visibility of Moiré pattern in the density profile, even for exceptionally weak
lattice potentials. The Moiré pattern can be enhanced similarly by increasing the
lattice depth, which, however, also induces droplet
diffusion characterized by a spreading density profile. Furthermore, we demonstrate a dynamical generation of Moiré pattern by dragging a small droplet through a moving
lattice. At appropriate velocities, the droplet undergoes bifurcation and exhibits pronounced Moiré pattern within periodic time intervals. Our results establish the ultracold droplet as a compelling platform for simulating interacting Moiré physics, particularly the interplay between Moiré
lattice and bound-state formation.
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Mesoscale and Nanoscale Physics
Conductance of silicon nanotube junctions in high magnetic fields
Teresa Kulka, Juan Alberto Canché-Martín, Irina V. Lebedeva et al. (+2 more)
We investigate coherent
quantum transport through silicon nanotube (SiNT) junctions in high
magnetic fields up to 60 T using a tight-binding model combined with the non-
equilibrium Green's function formalism, and
magnetic field included via Peierls substitution. We consider junctions of metallic nanotubes (6,0)+(6,0) and semiconducting ones (9,9)+(9,9), and examine the effects of the overlap length, inter-tube distance,
magnetic-field direction, and field strength on the electronic transmission. In contrast to carbon nanotube junctions, the SiNT systems exhibit irregular transmission oscillations and do not show the emergence of highly conductive gateway states. The transmission is substantially more sensitive to a
magnetic field perpendicular to the nanotube axis than to a parallel field, while increasing the field strength progressively modifies the transmission spectrum. Increasing the overlap length results in more frequent transmission oscillations, whereas increasing the inter-tube distance modifies their positions and amplitudes without changing their overall character. Generally, similar trends are observed for both types of junctions, involving metallic and semiconducting nanotubes. However, in the junction of semiconducting nanotubes, one observes peculiar additional field-dependent in-gap transmission features. These results demonstrate that the
magnetic-field response of SiNT junctions is strongly governed by their geometry and differs qualitatively from that of pristine carbon nanotube junctions.
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All authors Teresa Kulka, Juan Alberto Canché-Martín, Irina V. Lebedeva, Jacek A. Majewski, Karolina Z. Milowska