arXiv subjects

Peter P. Orth

Publications and source records attributed to Peter P. Orth.

At least 73 records · Page 4Linked to original sources

arXiv2018

Nodeless superconductivity in type-II Dirac semimetal PdTe2: low-temperature London penetration depth and symmetry analysis

Superconducting gap structure was probed in type-II Dirac semimetal PdTe$_2$ by measuring the London penetration depth using tunnel diode resonator technique. At low temperatures, the data for two samples are well described by weak coupling exponential fit yielding $λ(T=0)=230$~nm as the only fit parameter at a fixed $Δ(0)/T_c\approx 1.76$, and the calculated superfluid density is consistent with a fully gapped superconducting state characterized by a single gap scale. Electrical resistivity measurements for in-plane and inter-plane current directions find very low and nearly temperature-independent normal- state anisotropy. The temperature dependence of resistivity is typical for conventional phonon scattering in metals. We compare these experimental results with expectations from a detailed theoretical symmetry analysis and reduce the number of possible superconducting pairing states in PdTe$_2$ to only three nodeless candidates: a regular, topologically trivial, $s$-wave pairing, and two distinct odd-parity triplet states that both can be topologically non-trivial depending on the microscopic interactions driving the superconducting instability.

cond-mat.supr-con↗

arXiv2017

Extremely large magnetoresistance and Kohler's rule in PdSn4: a complete study of thermodynamic, transport and band structure properties

The recently discovered material PtSn$_4$ is known to exhibit extremely large magnetoresistance (XMR) that also manifests Dirac arc nodes on the surface. PdSn$_4$ is isostructure to PtSn$_4$ with same electron count. We report on the physical properties of high quality single crystals of PdSn$_4$ including specific heat, temperature and magnetic field dependent resistivity and magnetization, and electronic band structure properties obtained from angle resolved photoemission spectroscopy (ARPES). We observe that PdSn$_4$ has physical properties that are qualitatively similar to those of PtSn$_4$, but find also pronounced differences. Importantly, the Dirac arc node surface state of PtSn$_4$ is gapped out for PdSn$_4$. By comparing these similar compounds, we address the origin of the extremely large magnetoresistance in PdSn$_4$ and PtSn$_4$; based on detailed analysis of the magnetoresistivity, $ρ(H,T)$, we conclude that neither carrier compensation nor the Dirac arc node surface state are primary reason for the extremely large magnetoresistance. On the other hand, we find that surprisingly Kohler's rule scaling of the mangnetoresistance, which describes a self-similarity of the field induced orbital electronic motion across different length scales and is derived for a simple electronic response of metals to applied in a magnetic field is obeyed over the full range of temperatures and field strengths that we explore.

cond-mat.str-el↗

arXiv2017

Controlling competing orders via non-equilibrium acoustic phonons: emergence of anisotropic electronic temperature

Ultrafast perturbations offer a unique tool to manipulate correlated systems due to their ability to promote transient behaviors with no equilibrium counterpart. A widely employed strategy is the excitation of coherent optical phonons, as they can cause significant changes in the electronic structure and interactions on short time scales. Here, we explore a promising alternative route: the non-equilibrium excitation of acoustic phonons. We demonstrate that it leads to the remarkable phenomenon of a momentum-dependent temperature, by which electronic states at different regions of the Fermi surface are subject to distinct local temperatures. Such an anisotropic electronic temperature can have a profound effect on the delicate balance between competing ordered states in unconventional superconductors, opening a novel avenue to control correlated phases.

cond-mat.supr-con↗

arXiv2017

Dynamic Elastoresistivity Evidence for Slow Nematic Fluctuations in BaFe$_2$As$_2$

An instrumentation problem with the signal acquisition at high frequencies was discovered and we no longer believe that the experimental data presented in the manuscript, showing a frequency enhancement of the elastoresistivity, are correct. After correcting the problem, the elastoresistivity data is frequency independent in the range investigated. Therefore, the authors have withdrawn this submission. We would like to thank Alex Hristov, Johanna Palmstrom, Josh Straquadine and Ian Fisher (Stanford) for the kind discussions and assistance we received which helped us identify these problems.

cond-mat.str-el↗

arXiv2016

Topology of a dissipative spin: dynamical Chern number, bath induced non-adiabaticity and a quantum dynamo effect

We analyze the topological deformations of a spin-1/2 in an effective magnetic field induced by an ohmic quantum dissipative environment at zero temperature. From Bethe Ansatz results and a variational approach, we confirm that the Chern number is preserved in the delocalized phase for $α<1$. We report a divergence of the Berry curvature at the equator when $α_c=1$ that appears at the localization Kosterlitz-Thouless quantum phase transition in this model. Recent experiments in quantum circuits have engineered non-equilibrium protocols in time to access topological properties at equilibrium from the measure of the (quasi-)adiabatic out-of-equilibrium spin expectation values. Applying a numerically exact stochastic Schrödinger equation we find that, for a fixed sweep velocity, the bath induces a crossover from (quasi-)adiabatic to non-adiabatic dynamical behavior when the spin bath coupling increases. We also investigate the particular regime $H/ω_c \ll v/H \ll 1$, where the dynamical Chern number observable built from out-of-equilibrium spin expectation values vanishes at $α=1/2$. In this regime, the mapping to an interacting resonance level model enables us to characterize the evolution of the dynamical Chern number in the vicinity of $α=1/2$. Then, we provide an intuitive physical explanation of the breakdown of adiabaticity in analogy to the Faraday effect in electromagnetism. We demonstrate that the driving of the spin leads to the production of a large number of bosonic excitations in the bath, which in return strongly affect the spin dynamics. Finally, we quantify the spin-bath entanglement and build an analogy with an effective model at thermal equilibrium.

cond-mat.mes-hall↗

arXiv2016

Percolation via combined electrostatic and chemical doping in complex oxide films

Stimulated by experimental advances in electrolyte gating methods, we investigate theoretically percolation in thin films of inhomogenous complex oxides, such as La$_{1-x}$Sr$_{x}$CoO$_{3}$ (LSCO), induced by a combination of bulk chemical and surface electrostatic doping. Using numerical and analytical methods, we identify two mechanisms that describe how bulk dopants reduce the amount of electrostatic surface charge required to reach percolation: (i) bulk-assisted surface percolation, and (ii) surface-assisted bulk percolation. We show that the critical surface charge strongly depends on the film thickness when the film is close to the chemical percolation threshold. In particular, thin films can be driven across the percolation transition by modest surface charge densities \emph{via} surface-assisted bulk percolation. If percolation is associated with the onset of ferromagnetism, as in LSCO, we further demonstrate that the presence of critical magnetic clusters extending from the film surface into the bulk results in considerable volume enhancement of the saturation magnetization, with pronounced experimental consequences. These results should significantly guide experimental work seeking to verify gate-induced percolation transitions in such materials.

cond-mat.mes-hall↗

arXiv2015

Universal collisionless transport of graphene

The impact of the electron-electron Coulomb interaction on the optical conductivity of graphene has led to a controversy that calls into question the universality of collisionless transport in this and other Dirac materials. Using a lattice calculation that avoids divergences present in previous nodal Dirac approaches, our work settles this controversy and obtains results in quantitative agreement with experiment over a wide frequency range. We also demonstrate that dimensional regularization methods agree, as long as the scaling properties of the conductivity and the regularization of the theory in modified dimension are correctly implemented. Tight-binding lattice and nodal Dirac theory calculations are shown to coincide at low energies even when the non-zero size of the atomic orbital wave function is included, conclusively demonstrating the universality of the optical conductivity of graphene.

cond-mat.str-el↗

arXiv2015

Universal post-quench coarsening and quantum aging at a quantum critical point

The non-equilibrium dynamics of a system that is located in the vicinity of a quantum critical point is affected by the critical slowing down of order-parameter correlations with the potential for novel out-of-equilibrium universality. After a quantum quench, i.e. a sudden change of a parameter in the Hamiltonian such a system is expected to almost instantly fall out of equilibrium and undergo aging dynamics, i.e. dynamics that depends on the time passed since the quench. Investigating the quantum dynamics of a $N$-component $φ^{4}$-model coupled to an external bath, we determine this universal aging and demonstrate that the system undergoes a coarsening, governed by a critical exponent that is unrelated to the equilibrium exponents of the system. We analyze this behavior in the large-$N$ limit, which is complementary to our earlier renormalization group analysis, allowing in particular the direct investigation of the order-parameter dynamics in the symmetry broken phase and at the upper critical dimension. By connecting the long time limit of fluctuations and response, we introduce a distribution function that shows that the system remains non-thermal and exhibits quantum coherence even on long timescales.

cond-mat.str-el↗

arXiv2015

Emergent Power-Law Phase in the 2D Heisenberg Windmill Antiferromagnet: A Computational Experiment

In an extensive computational experiment, we test Polyakov's conjecture that under certain circumstances an isotropic Heisenberg model can develop algebraic spin correlations. We demonstrate the emergence of a multi-spin $\text{U(1)}$ order parameter in a Heisenberg antiferromagnet on interpenetrating honeycomb and triangular lattices. The correlations of this relative phase angle are observed to decay algebraically at intermediate temperatures in an extended critical phase. Using finite-size scaling, we show that both phase transitions are of the Berezinskii-Kosterlitz-Thouless type and at lower temperatures, we find long-range $\mathbb{Z}_6$ order.

cond-mat.str-el↗

arXiv2015

Luminescence and Squeezing of a Superconducting Light Emitting Diode

We investigate a semiconductor $p$-$n$ junction in contact with superconducting leads that is operated under forward bias as a light-emitting diode. The presence of superconductivity results in a significant increase of the electroluminescence in a certain frequency window. We demonstrate that the tunneling of Cooper pairs induces an additional luminescence peak on resonance. There is a transfer of superconducting to photonic coherence which results in the emission of entangled photon pairs and squeezing of the fluctuations in the quadrature amplitudes of the emitted light. The squeezing angle can be electrically manipulated by changing the relative phase of the order parameters in the superconductors. We finally derive the conditions for lasing in the system and show that the laser threshold is reduced due to superconductivity. This shows how macroscopic coherence of a superconductor can be used to control the properties of light.

cond-mat.mes-hall↗

arXiv2015

Universal post-quench prethermalization at a quantum critical point

We consider an open system near a quantum critical point that is suddenly moved towards the critical point. The bath-dominated diffusive non-equilibrium dynamics after the quench is shown to follow scaling behavior, governed by a critical exponent that emerges in addition to the known equilibrium critical exponents. We determine this exponent and show that it describes universal prethermalized coarsening dynamics of the order parameter in an intermediate time regime. Implications of this quantum critical prethermalization are a powerlaw rise of order and correlations after an initial collapse of the equilibrium state and a crossover to thermalization that occurs arbitrarily late for sufficiently shallow quenches.

cond-mat.str-el↗

arXiv2014

Classical Heisenberg and planar spin models on the windmill lattice

We investigate the classical Heisenberg and planar (XY) models on the windmill lattice. The windmill lattice is formed out of two widely occurring lattice geometries: a triangular lattice is coupled to its dual honeycomb lattice. Using a combination of iterative minimization, heat-bath Monte Carlo simulations and analytical calculations, we determine the complete ground state phase diagram of both models and find the exact energies of the phases. The phase diagram shows a rich phenomenology due to competing interactions and hosts, in addition to collinear and various coplanar phases, also intricate non-coplanar phases. We briefly outline different paths to an experimental realization of these spin models. Our extensive study provides a starting point for the investigation of quantum and thermal fluctuation effects.

cond-mat.str-el↗

arXiv2014

Quantum Dynamics of the Driven and Dissipative Rabi Model

The Rabi model considers a two-level system (or spin-1/2) coupled to a quantized harmonic oscillator and describes the simplest interaction between matter and light. The recent experimental progress in solid-state circuit quantum electrodynamics has engendered theoretical efforts to quantitatively describe the mathematical and physical aspects of the light-matter interaction beyond the rotating wave approximation. We develop a stochastic Schrödinger equation approach which enables us to access the strong-coupling limit of the Rabi model and study the effects of dissipation, and AC drive in an exact manner. We include the effect of ohmic noise on the non-Markovian spin dynamics resulting in Kondo-type correlations, as well as cavity losses. We compute the time evolution of spin variables in various conditions. As a consideration for future work, we discuss the possibility to reach a steady state with one polariton in realistic experimental conditions.

cond-mat.mes-hall↗

arXiv2014

Dimensional crossover and cold-atom realization of topological Mott insulators

We propose a cold-atom setup which allows for a dimensional crossover from a two-dimensional quantum spin Hall insulating phase to a three-dimensional strong topological insulator by tuning the hopping between the layers. We further show that additional Hubbard onsite interactions can give rise to spin liquid-like phases: weak and strong topological Mott insulators. They represent the celebrated paradigm of a quantum state of matter which merely exists because of the interplay of the non-trivial topology of the band structure and strong interactions. While the theoretical understanding of this phase has remained elusive, our proposal shall help to shed some light on this exotic state of matter by paving the way for a controlled experimental investigation in optical lattices.

cond-mat.quant-gas↗

arXiv2014

Manipulation of a two-photon pump in superconductor - semiconductor heterostructures

We investigate the photon statistics, entanglement and squeezing of a pn-junction sandwiched between two superconducting leads, and show that such an electrically-driven photon pump generates correlated and entangled pairs of photons. In particular, we demonstrate that the squeezing of the fluctuations in the quadrature amplitudes of the emitted light can be manipulated by changing the relative phase of the order parameters of the superconductors. This reveals how macroscopic coherence of the superconducting state can be used to tailor the properties of a two-photon state.

cond-mat.mes-hall↗

arXiv2013

Emergent Criticality and Friedan Scaling in a 2D Frustrated Heisenberg Antiferromagnet

We study a two-dimensional frustrated Heisenberg antiferromagnet on the windmill lattice consisting of triangular and dual honeycomb lattice sites. In the classical ground state the spins on different sublattices are decoupled, but quantum and thermal fluctuations drive the system into a coplanar state via an "order from disorder" mechanism. We obtain the finite temperature phase diagram using renormalization group approaches. In the coplanar regime, the relative U$(1)$ phase between the spins on the two sublattices decouples from the remaining degrees of freedom, and is described by a six-state clock model with an emergent critical phase. At lower temperatures the system enters a $\mathbb{Z}_6$ broken phase with long-range phase correlations. We derive these results by two distinct renormalization group approaches to two-dimensional magnetism: by Wilson-Polyakov scaling and by Friedan's geometric approach to nonlinear sigma models where the scaling of the spin-stiffnesses is governed by the Ricci flow of a 4D metric tensor.

cond-mat.str-el↗

arXiv2013

Correlated Topological Phases and Exotic Magnetism with Ultracold Fermions

Motivated by the recent progress in engineering artificial non-Abelian gauge fields for ultracold fermions in optical lattices, we investigate the time-reversal-invariant Hofstadter-Hubbard model. We include an additional staggered lattice potential and an artificial Rashba--type spin-orbit coupling term available in experiment. Without interactions, the system can be either a (semi)-metal, a normal or a topological insulator, and we present the non-Abelian generalization of the Hofstadter butterfly. Using a combination of real-space dynamical mean-field theory (RDMFT), analytical arguments, and Monte-Carlo simulations we study the effect of strong on-site interactions. We determine the interacting phase diagram, and discuss a scenario of an interaction-induced transition from normal to topological insulator. At half-filling and large interactions, the system is described by a quantum spin Hamiltonian, which exhibits exotic magnetic order due to the interplay of Rashba--type spin-orbit coupling and the artificial time-reversal-invariant magnetic field term. We determine the magnetic phase diagram: both for the itinerant model using RDMFT and for the corresponding spin model in the classical limit using Monte-Carlo simulations.

cond-mat.quant-gas↗

arXiv2013

Non-perturbative stochastic method for driven spin-boson model

We introduce and apply a numerically exact method for investigating the real-time dissipative dynamics of quantum impurities embedded in a macroscopic environment beyond the weak-coupling limit. We focus on the spin-boson Hamiltonian that describes a two-level system interacting with a bosonic bath of harmonic oscillators. This model is archetypal for investigating dissipation in quantum systems and tunable experimental realizations exist in mesoscopic and cold-atom systems. It finds abundant applications in physics ranging from the study of decoherence in quantum computing and quantum optics to extended dynamical mean-field theory. Starting from the real-time Feynman-Vernon path integral, we derive an exact stochastic Schrödinger equation that allows to compute the full spin density matrix and spin-spin correlation functions beyond weak coupling. We greatly extend our earlier work (P. P. Orth, A. Imambekov, and K. Le Hur, Phys. Rev. A {\bf 82}, 032118 (2010)) by fleshing out the core concepts of the method and by presenting a number of interesting applications. Methodologically, we present an analogy between the dissipative dynamics of a quantum spin and that of a classical spin in a random magnetic field. This analogy is used to recover the well-known non-interacting-blip-approximation in the weak-coupling limit. We explain in detail how to compute spin-spin autocorrelation functions. As interesting applications of our method, we explore the non-Markovian effects of the initial spin-bath preparation on the dynamics of the coherence $σ^x(t)$ and of $σ^z(t)$ under a Landau-Zener sweep of the bias field. We also compute to a high precision the asymptotic long-time dynamics of $σ^z(t)$ without bias and demonstrate the wide applicability of our approach by calculating the spin dynamics at non-zero bias and different temperatures.

cond-mat.str-el↗