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Shi, Zhenzhong; Shi, Xiaoyan; Popović, Dragana

doi:10.1103/physrevb.94.134503

Cited by 6 publications

(11 citation statements)

References 59 publications

(93 reference statements)

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“…With decreasing T , δR 2 / R 2 shoots up because of the onset of superconducting fluctuations. This has been seen before in many different superconducting systems and will not be discussed further in this letter [27][28][29].…”

supporting

confidence: 55%

Quantum Phase Transition in Few-Layer NbSe2 Probed through Quantized Conductance Fluctuations

et al. 2017

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We present the first observation of dynamically modulated quantum phase transition (QPT) between two distinct charge density wave (CDW) phases in 2-dimensional 2H-NbSe2. There is recent spectroscopic evidence for the presence of these two quantum phases, but its evidence in bulk measurements remained elusive. We studied suspended, ultra-thin 2H-NbSe2 devices fabricated on piezoelectric substrates -with tunable flakes thickness, disorder level and strain. We find a surprising evolution of the conductance fluctuation spectra across the CDW temperature: the conductance fluctuates between two precise values, separated by a quantum of conductance. These quantized fluctuations disappear for disordered and on-substrate devices. With the help of mean-field calculations, these observations can be explained as to arise from dynamical phase transition between the two CDW states. To affirm this idea, we vary the lateral strain across the device via piezoelectric medium and map out the phase diagram near the quantum critical point (QCP). The results resolve a long-standing mystery of the anomalously large spectroscopic gap in NbSe2.Despite intensive research over several decades, charge density waves (CDW) continue to remain at the forefront of modern condensed matter physics [1][2][3]. CDW in quasi-one dimension is understood to arise from Peierls mechanism -an inherent instability of a coupled electronphonon system which creates a gap in the single-particle excitation spectrum leading to the emergence of a collective mode formed of electron-hole pairs [4]. In higher dimensions this electron-phonon interaction induced renormalization of the lattice wave vectors is often not enough to give rise to CDW [5][6][7][8][9][10][11][12][13][14]. One of the best known examples is 2H-NbSe 2 , where the mechanism of CDW is still widely debated [15][16][17][18][19][20]. It has been suggested that the origin may lie in the strong momentum and orbital dependence of the electron-phonon coupling [18,19]. A natural consequence of this is the sensitivity of the CDW order to lattice perturbations. This has recently been verified by Scanning Tunneling Microscopy (STM) measurements, which find the existence of 1Q striped quantum phase competing with the standard 3Q phase in locally strained regions [40]. The tri-directional 3Q phase respects the three-fold lattice symmetry and has a periodicity Q 0.328G 0 , where G 0 is the reciprocal lattice vector. The 1Q is a linear phase with a periodicity Q (2/7)G 0 [40]. Calculations indicate that, for T T CDW , the system is very close to a quantum critical point separating these two phases and any small perturbation, like local strain, can induce a quantum phase transition (QPT) between these two [20,22,23]. There are however, no direct experimental evidences of this QPT.We probe for the possible existence of QPT in ultrathin, suspended 2H-NbSe 2 devices through time dependent conductance fluctuation spectroscopy [39]. We find that, for devices where the strain is dynamic, the electrical conductance fluc...

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confidence: 55%

Quantum Phase Transition in Few-Layer NbSe2 Probed through Quantized Conductance Fluctuations

et al. 2017

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“…As a consequence of this, global HXY spin-twist excitations generated by local HXY charge (or spin-vortex) dynamics are ergodically excluded in the low-temperature phase. This may explain the recently measured [36] non-ergodic dynamics in layered cuprates at the superconducting transition, where the spins become the phases of the condensate wavefunction.…”

Section: Discussionmentioning

confidence: 71%

“…Topological sectors are global topological defects in the lattice electric field, which can be generated by charges tracing closed paths around the torus. This idea has subsequently been extended in detail to a model of strongly interacting Bosons in a ring lattice [35] and has been suggested as a mechanism for the nonergodic dynamics observed experimentally in layered cuprates at the superconducting transition [36]. Hence, the lattice electric-field method allows us to identify the nature of the topological-sector fluctuations of the HXY model, which are of direct relevance to fluctuations in experimental spin systems and condensates.…”

Section: Introductionmentioning

confidence: 99%

An electric-field representation of the harmonic XY model

Faulkner,

Bramwell,

Holdsworth

2016

Preprint

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The two-dimensional harmonic XY (HXY) model is a spin model in which the classical spins interact via a piecewise parabolic potential. We argue that the HXY model should be regarded as the canonical classical lattice spin model of phase fluctuations in two-dimensional condensates, as it is the simplest model that guarantees the modular symmetry of the experimental systems.Here we formulate a lattice electric-field representation of the HXY model and contrast this with an analogous representation of the Villain model and the twodimensional Coulomb gas with a purely rotational auxiliary field. We find that the HXY model is a spin-model analogue of a lattice electric-field model of the Coulomb gas with an auxiliary field, but with a temperature-dependent vacuum (electric) permittivity that encodes the coupling of the spin vortices to their background spin-wave medium. The spin vortices map to the Coulomb charges, while the spin-wave fluctuations correspond to auxiliary-field fluctuations. The coupling explains the striking differences in the high-temperature asymptotes of the specific heats of the HXY model and the Coulomb gas with an auxiliary field. Our results elucidate the propagation of effective long-range interactions throughout the HXY model (whose interactions are purely local) by the lattice electric fields. They also imply that global spin-twist excitations (topologicalsector fluctuations) generated by local spin dynamics are ergodically excluded in the low-temperature phase. We discuss the relevance of these results to condensate physics.

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“…Symmetry-breaking phenomena have been measured, however, on experimental timescales in a diverse array of BKT systems [17][18][19][20][21][22][23][24][25][26][27][28][29], including on very long timescales [18] and in systems that approach idealised U (1) symmetry [19,20]. This suggests that the rather elegant mathematical formalism of spontaneous symmetry breaking may be too restrictive to account for all physical observations.…”

mentioning

confidence: 99%

“…This suggests that the rather elegant mathematical formalism of spontaneous symmetry breaking may be too restrictive to account for all physical observations. For example, recent measurements of the electrical resistance of films of lanthanum strontium copper oxide (LSCO) revealed an onset of nonergodic roughening of its probability density function (PDF) as the superconducting transition is approached from high temperature [18]. As condensate-phase differences induce resistance and the experimental timescale was on the order of ten hours, this is likely to be due to increasingly large regions of symmetrybroken (and therefore persistent on some significant timescale) condensate-phase coherence during the approach to the transition.…”

mentioning

confidence: 99%

General symmetry breaking at a topological phase transition

Faulkner¹

2022

Preprint

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Evidence for correlated dynamics near the Berezinskii-Kosterlitz-Thouless-like transition in highly underdopedLa2−xSrxCuO4

Cited by 6 publications

References 59 publications

Quantum Phase Transition in Few-Layer NbSe2 Probed through Quantized Conductance Fluctuations

Quantum Phase Transition in Few-Layer NbSe2 Probed through Quantized Conductance Fluctuations

An electric-field representation of the harmonic XY model

General symmetry breaking at a topological phase transition

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