Today's
#arXivsummary:
https://arxiv.org/abs/2311.06350 by Romen et. al. Authors investigate deconfined quantum critical points in the long-range, anisotropic Heisenberg chain. Model undergoes a continuous phase transition from valence bond solid to an antiferromagnet. Long-range interactions are irrelevant & transition is well described by a double frequency sine-Gordon model.
#CondMat #arXiv_2311_06350
Deconfined Quantum Criticality in the long-range, anisotropic Heisenberg Chain
Deconfined quantum criticality describes continuous phase transitions that are not captured by the Landau-Ginzburg paradigm. Here, we investigate deconfined quantum critical points in the long-range, anisotropic Heisenberg chain. With matrix product state simulations, we show that the model undergoes a continuous phase transition from a valence bond solid to an antiferromagnet. We extract the critical exponents of the transition and connect them to an effective field theory obtained from bosonization techniques. We show that beyond stabilizing the valance bond order, the long-range interactions are irrelevant and the transition is well described by a double frequency sine-Gordon model. We propose how to realize and probe deconfined quantum criticality in our model with trapped-ion quantum simulators.
Today's
#arXivsummary:
https://arxiv.org/abs/2311.04266 by Radzihovsky. Author points out a simple and generic mechanism for a thermally-driven reentrant supersolidity. Mechanism reduces to a re-enterant low-temperature normal-superfluid transition.
#CondMat #arXiv_2311_04266Reentrant supersolidity
A "supersolid" -- a crystal that exhibits an off-diagonal long-range order and a superflow -- has been a subject of much research since its first proposal [Andreev and Lifshitz 1969], but has not been realized as a ground state of short-range interacting bosons in a continuum. In this note I point out a simple and generic mechanism for a thermally-driven reentrant supersolidity, and discuss challenges of experimental realization of this idea. In the limit of bosons in a periodic potential, this mechanism reduces to a {\em reentrant} low-temperature normal-superfluid transition, that should be accessible to simulations and in current experiments on bosonic atoms in an optical periodic potential.
Today's
#arXivsummary:
https://arxiv.org/abs/2311.02155 by Pak et. al. Authors show that the PT-symmetry stabilizes the Hopf invariant in the Hopf insulator even in the presence of non-Hermiticity. Zak phase remains quantized.
#CondMat #arXiv_2311_02155PT-symmetric Non-Hermitian Hopf Metal
Hopf insulator is a representative class of three-dimensional topological
insulators beyond the standard topological classification methods based on
K-theory. In this letter, we discover the metallic counterpart of the Hopf
insulator in the non-Hermitian systems. While the Hopf invariant is not a
stable topological index due to the additional non-Hermitian degree of freedom,
we show that the PT-symmetry stabilizes the Hopf invariant even in the presence
of the non-Hermiticity. In sharp contrast to the Hopf insulator phase in the
Hermitian counterpart, we discover an interesting result that the non-Hermitian
Hopf bundle exhibits the topologically protected non-Hermitian degeneracy,
characterized by the two-dimensional surface of exceptional points. Despite the
non-Hermiticity, the Hopf metal has the quantized Zak phase, which results in
bulk-boundary correspondence by showing drumhead-like surface states at the
boundary. Finally, we show that, by breaking PT-symmetry, the nodal surface
deforms into the knotted exceptional lines. Our discovery of the Hopf metal
phase firstly confirms the existence of the non-Hermitian topological phase
outside the framework of the standard topological classifications.
Today's
#arXivsummary:
https://arxiv.org/abs/2310.11236 by Misawa. Author's work suggests that quasiparticles in the normal state of high-Tc cuprate superconductors behave as a 3D Fermi liquid. Logarithmic formula as a function of T emerges in transport quantities and thermodynamics results from quasiparticle interactions.
#CondMat #arXiv_2310_11236The 3-dimensional Fermi liquid description for the normal state of cuprate superconductors
The quasiparticles in the normal state of cuprate superconductors have been shown to behave universally as a 3-dimensional Fermi liquid. Because of interactions and the presence of the Fermi surfaces (or Fermi energies), the quasiparticle energy contains, as a function of the momentum $\boldmath{p}$, a term of the form $(p-p_0)^3 \ln ( | p-p_0 | / p_0 )$, where $p = | \boldmath{p} |$ and $p_0$ is the Fermi momentum. The electronic specific heat coefficient $γ(T)$, electrical resistivity, Hall coefficient and thermoelectric power divided by temperature $T$, follow the logarithmic formula $a - b T^2 \ln ( T/T^*) $, $a$, $b$, and $T^*$ being constant. Singularities in the Landau $f$-function produce the $T^2 \ln T$ dependence of the magnetic susceptibility $χ(T)$, and Knight shift, which gives rise to the phenomenon of the susceptibility maximum. The logarithmic $T$-dependence of the transport properties arises exclusively from the impurity scattering in 3-dimensional (3D) systems, but does not from the electron-electron scattering in 2D systems. The above logarithmic formula has been shown to explain universally the experimental data for the normal state of all cuprate superconductors. The decrease of $γ(T)$ or $χ(T)$ with decreasing $T$ is not due to the appearance of pseudogap or spin gap but due to its $T^2 \ln T$ variation.
Today's
#arXivsummary:
https://arxiv.org/abs/2310.09324 by Sun. Authors show that an indirect exchange interaction between spin impurities can be controlled by a dissipationless supercurrent with just a conventional superconductor and two spin impurities placed on its surface.
#CondMat #arXiv_2310_09324Supercurrent-induced spin switching via indirect exchange interaction
Localized spins of single atoms adsorbed on surfaces have been proposed as building blocks for spintronics and quantum computation devices. However, identifying a way to achieve current-induced switching of spins with very low dissipation is an outstanding challenge with regard to practical applications. Here, we show that the indirect exchange interaction between spin impurities can be controlled by a dissipationless supercurrent. All that is required is a conventional superconductor and two spin impurities placed on its surface. No triplet Cooper pairs or exotic material choices are needed. This finding provides a new and accessible way to achieve the long-standing goal of supercurrent-induced spin switching.
Today's
#arXivsummary:
https://arxiv.org/abs/2310.07978 by Chen et. al. Authors study Anderson localization in disordered tight-binding models on hyperbolic lattices. Numerically show the existence of an Anderson localization transition on the {8,3} & {8,8} lattices.
#CondMat #arXiv_2310_07978Anderson localization transition in disordered hyperbolic lattices
We study Anderson localization in disordered tight-binding models on hyperbolic lattices. Such lattices are geometries intermediate between ordinary two-dimensional crystalline lattices, which localize at infinitesimal disorder, and Bethe lattices, which localize at strong disorder. Using state-of-the-art computational group theory methods to create large systems, we approximate the thermodynamic limit through appropriate periodic boundary conditions and numerically demonstrate the existence of an Anderson localization transition on the $\{8,3\}$ and $\{8,8\}$ lattices. We find unusually large critical disorder strengths, determine critical exponents, and observe a strong finite-size effect in the level statistics.
Today's
#arXivsummary:
https://arxiv.org/abs/2310.06891 by Kao et. al. Authors study the dynamical response of vacancy-induced quasiparticle excitations in a site-diluted Kitaev spin liquid in the presence of a magnetic field. STM response is shown to be sensitive to the local flux configuration, magnetic field strength, and vacancy concentration.
#CondMat #arXiv_2310_06891Dynamics of vacancy-induced modes in the non-Abelian Kitaev spin liquid
We study the dynamical response of vacancy-induced quasiparticle excitations in the site-diluted Kitaev spin liquid with a magnetic field. Due to the flux-binding effect and the emergence of dangling Majorana fermions around each spin vacancy, the low-energy physics is governed by a set of vacancy-induced quasi-zero-energy modes. These localized modes result in unique characteristics of the dynamical spin correlation functions, which intriguingly mimic the single-quasiparticle density of states and further exhibit a quasi-zero-frequency peak. By recognizing the potential observability of these local correlation functions via scanning tunneling microscopy (STM), we show how the STM response is sensitive to the local flux configuration, the magnetic field strength, and the vacancy concentration. Constructing a simple model of the localized modes, we also elucidate how the local correlation functions can be interpreted in terms of the hybridization between these modes.
Today's
#arXivsummary:
https://arxiv.org/abs/2310.06748 by Shankar & Maciejko. Authors utilize semiclassical instanton methods not relying on conformal invariance to construct monopole operators directly in (2+1)D spacetime as instanton-induced 't Hooft vertices, as applied to the Dirac liquid. Instanton-based approach can determine monopole quantum numbers on bipartite lattices.
#CondMat #arXiv_2310_06748Monopoles in Dirac spin liquids and their symmetries from instanton calculus
The Dirac spin liquid (DSL) is a two-dimensional (2D) fractionalized Mott insulator featuring massless Dirac spinon excitations coupled to a compact $U(1)$ gauge field, which allows for flux-tunneling instanton events described by magnetic monopoles in (2+1)D Euclidean spacetime. The state-operator correspondence of conformal field theory has been used recently to define associated monopole operators and determine their quantum numbers, which encode the microscopic symmetries of conventional ordered phases proximate to the DSL. In this work, we utilize semiclassical instanton methods not relying on conformal invariance to construct monopole operators directly in (2+1)D spacetime as instanton-induced 't Hooft vertices, i.e., fermion-number-violating effective interactions originating from zero modes of the Euclidean Dirac operator in an instanton background. In the presence of a flavor-adjoint fermion mass, resummation of the instanton gas is shown to select the correct monopole to be proliferated, in accordance with predictions of the state-operator correspondence. We also show that our instanton-based approach is able to determine monopole quantum numbers on bipartite lattices.
Today's
#arXivsummary:
https://arxiv.org/abs/2310.03452 by Dyke et. al. Authors excite amplitude oscillations in an atomic Fermi gas with resonant interactions via an interaction quench. Time-resolved response of the atom cloud measured, which reveals amplitude oscillations at twice the frequency of the gap.
#CondMat #arXiv_2310_03452Higgs oscillations in a unitary Fermi superfluid
Symmetry-breaking phase transitions are central to our understanding of states of matter. When a continuous symmetry is spontaneously broken, new excitations appear that are tied to fluctuations of the order parameter. In superconductors and fermionic superfluids, the phase and amplitude can fluctuate independently, giving rise to two distinct collective branches. However, amplitude fluctuations are difficult to both generate and measure, as they do not couple directly to the density of fermions and have only been observed indirectly to date. Here, we excite amplitude oscillations in an atomic Fermi gas with resonant interactions by an interaction quench. Exploiting the sensitivity of Bragg spectroscopy to the amplitude of the order parameter, we measure the time-resolved response of the atom cloud, directly revealing amplitude oscillations at twice the frequency of the gap. The magnitude of the oscillatory response shows a strong temperature dependence, and the oscillations appear to decay faster than predicted by time-dependent BCS theory applied to our experimental setup.
Today's
#arXivsummary:
https://arxiv.org/abs/2310.02910 by Zhao et. al. Authors develop expressions for non-local resistances of hybrid quantum Hall-superconducting devices. Superconducting phase coherence is not maintained over micron-scale graphene devices.
#CondMat #arXiv_summary_2310_02910Non-local transport measurements in hybrid quantum Hall - superconducting devices
There has been a growing interest in hybrid quantum Hall (QH) superconductor devices, driven by the prospect to realize exotic ground states and excitations with non-abelian exchange statistics. While the existing experiments clearly demonstrate Andreev coupling between the edge states and the superconductors, the question remains whether the quantum coherence could propagate between several superconducting contacts via chiral channels. To answer this question, we have first extended the Landauer-Büttiker (LB) formalism to samples with one superconducting contact and found a remarkable agreement within a series of measurements related to each other via LB-type formulae. We have then switched to the case of multiple superconducting contacts, and found that we can describe the measurements self-consistently if we neglect the superconducting phase coherence between multiple contacts. We interpret this result as a negative answer to the question posed above: the phase correlations between multiple superconducting contacts are not established via micron-long quantum Hall edge states. Looking forward, our approach may find applications in the broader field of topological superconductivity and proximal structures. Possible violations of the self-consistency tests presented here may be used as an indication that superconducting phase coherence is induced in the quantum Hall edges.
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