scholarly journals Nematic quantum criticality in an Fe-based superconductor revealed by strain-tuning

Science ◽  
2021 ◽  
Vol 372 (6545) ◽  
pp. 973-977
Author(s):  
Thanapat Worasaran ◽  
Matthias S. Ikeda ◽  
Johanna C. Palmstrom ◽  
Joshua A. W. Straquadine ◽  
Steven A. Kivelson ◽  
...  
Keyword(s):  
Power Law ◽  
Structural Phase ◽  
Quantum Critical Point ◽  
Quantum Criticality ◽  
Conclusive Evidence ◽  
Tuning Parameter ◽  
Thermodynamic Quantities ◽  
Critical Fluctuations ◽  
Wide Range ◽  
Quantum Critical

Quantum criticality may be essential to understanding a wide range of exotic electronic behavior; however, conclusive evidence of quantum critical fluctuations has been elusive in many materials of current interest. An expected characteristic feature of quantum criticality is power-law behavior of thermodynamic quantities as a function of a nonthermal tuning parameter close to the quantum critical point (QCP). Here, we observed power-law behavior of the critical temperature of the coupled nematic/structural phase transition as a function of uniaxial stress in a representative family of iron-based superconductors, providing direct evidence of quantum critical nematic fluctuations in this material. These quantum critical fluctuations are not confined within a narrow regime around the QCP but rather extend over a wide range of temperatures and compositions.

scholarly journals Anomalous quantum criticality in the electron-doped cuprates

2019 ◽  
Vol 116 (13) ◽  
pp. 5991-5994 ◽  
Author(s):  
P. R. Mandal ◽  
Tarapada Sarkar ◽  
Richard L. Greene
Keyword(s):  
Low Temperature ◽  
Condensed Matter ◽  
Quantum Critical Point ◽  
Quantum Criticality ◽  
Cuprate Superconductor ◽  
Superconducting Transition ◽  
Critical Fluctuations ◽  
Quantum Critical Phenomena ◽  
Quantum Critical ◽  
Doping Range

In the physics of condensed matter, quantum critical phenomena and unconventional superconductivity are two major themes. In electron-doped cuprates, the low critical field (HC2) allows one to study the putative quantum critical point (QCP) at low temperature and to understand its connection to the long-standing problem of the origin of the high-TCsuperconductivity. Here we present measurements of the low-temperature normal-state thermopower (S) of the electron-doped cuprate superconductor La2−xCexCuO4(LCCO) fromx= 0.11–0.19. We observe quantum criticalS/Tversusln(1/T)behavior over an unexpectedly wide doping rangex= 0.15–0.17 above the QCP (x= 0.14), with a slope that scales monotonically with the superconducting transition temperature (TCwith H = 0). The presence of quantum criticality over a wide doping range provides a window on the criticality. The thermopower behavior also suggests that the critical fluctuations are linked withTC. Above the superconductivity dome, atx= 0.19, a conventional Fermi-liquidS∝Tbehavior is found forT≤40 K.

scholarly journals Magnetic field-driven quantum criticality in antiferromagnetic CePtIn4

2019 ◽  
Vol 116 (41) ◽  
pp. 20333-20338 ◽  
Author(s):  
Debarchan Das ◽  
Daniel Gnida ◽  
Piotr Wiśniewski ◽  
Dariusz Kaczorowski
Keyword(s):  
Magnetic Field ◽  
Tricritical Point ◽  
Condensed Matter ◽  
Quantum Critical Point ◽  
Quantum Criticality ◽  
Transition Line ◽  
First Order ◽  
Experimental Systems ◽  
Quantum Critical ◽  
Second Order Phase Transition

Physics of the quantum critical point is one of the most perplexing topics in current condensed-matter physics. Its conclusive understanding is forestalled by the scarcity of experimental systems displaying novel aspects of quantum criticality. We present comprehensive experimental evidence of a magnetic field-tuned tricritical point separating paramagnetic, antiferromagnetic, and metamagnetic phases in the compound CePtIn4. Analyzing field variations of its magnetic susceptibility, magnetoresistance, and specific heat at very low temperatures, we trace modifications of the antiferromagnetic structure of the compound. Upon applying a magnetic field of increasing strength, the system undergoes metamagnetic transitions which persist down to the lowest temperature investigated, exhibiting first-order–like boundaries separating magnetic phases. This yields a unique phase diagram where the second-order phase transition line terminates at a tricritical point followed by 2 first-order lines reaching quantum critical end points as T→ 0. Our findings demonstrate that CePtIn4 provides innovative perspective for studies of quantum criticality.

scholarly journals Power-law growth of time and strength of squeezing near a quantum critical point

2020 ◽  
Vol 102 (3) ◽  
Author(s):  
Deepti Sharma ◽  
Brijesh Kumar
Keyword(s):  
Critical Point ◽  
Power Law ◽  
Quantum Critical Point ◽  
Quantum Critical

scholarly journals Bose polarons near quantum criticality

Science ◽  
2020 ◽  
Vol 368 (6487) ◽  
pp. 190-194 ◽  
Author(s):  
Zoe Z. Yan ◽  
Yiqi Ni ◽  
Carsten Robens ◽  
Martin W. Zwierlein
Keyword(s):  
Critical Temperature ◽  
Quantum Critical Point ◽  
Spectral Width ◽  
Quantum Criticality ◽  
Einstein Condensate ◽  
Resonant Interactions ◽  
Bose Einstein Condensate ◽  
Modern Physics ◽  
Quantum Critical ◽  
Bose Einstein

The emergence of quasiparticles in interacting matter represents one of the cornerstones of modern physics. However, in the vicinity of a quantum critical point, the existence of quasiparticles comes under question. Here, we created Bose polarons near quantum criticality by immersing atomic impurities in a Bose-Einstein condensate (BEC) with near-resonant interactions. Using radiofrequency spectroscopy, we probed the energy, spectral width, and short-range correlations of the impurities as a function of temperature. Far below the superfluid critical temperature, the impurities formed well-defined quasiparticles. Their inverse lifetime, given by their spectral width, increased linearly with temperature at the so-called Planckian scale, consistent with quantum critical behavior. Close to the BEC critical temperature, the spectral width exceeded the impurity’s binding energy, signaling a breakdown of the quasiparticle picture.

scholarly journals Quantum critical scaling and fluctuations in Kondo lattice materials

2017 ◽  
Vol 114 (24) ◽  
pp. 6250-6255 ◽  
Author(s):  
Yi-feng Yang ◽  
David Pines ◽  
Gilbert Lonzarich
Keyword(s):  
Critical Point ◽  
Quantum Critical Point ◽  
Kondo Lattice ◽  
Critical Scaling ◽  
Critical Fluctuations ◽  
Lattice Materials ◽  
Heavy Electron ◽  
Logarithmic Scaling ◽  
Quantum Critical ◽  
Quantum Critical Scaling

We propose a phenomenological framework for three classes of Kondo lattice materials that incorporates the interplay between the fluctuations associated with the antiferromagnetic quantum critical point and those produced by the hybridization quantum critical point that marks the end of local moment behavior. We show that these fluctuations give rise to two distinct regions of quantum critical scaling: Hybridization fluctuations are responsible for the logarithmic scaling in the density of states of the heavy electron Kondo liquid that emerges below the coherence temperature T∗, whereas the unconventional power law scaling in the resistivity that emerges at lower temperatures below TQC may reflect the combined effects of hybridization and antiferromagnetic quantum critical fluctuations. Our framework is supported by experimental measurements on CeCoIn5, CeRhIn5, and other heavy electron materials.

scholarly journals Pressure-tuned quantum criticality in the antiferromagnetic Kondo semimetal CeNi2−δAs2

2015 ◽  
Vol 112 (44) ◽  
pp. 13520-13524 ◽  
Author(s):  
Yongkang Luo ◽  
F. Ronning ◽  
N. Wakeham ◽  
Xin Lu ◽  
Tuson Park ◽  
...  
Keyword(s):  
Electrical Transport ◽  
Carrier Density ◽  
Quantum Critical Point ◽  
Quantum Criticality ◽  
Kondo Lattice ◽  
Antiferromagnetic Order ◽  
Zero Temperature ◽  
Electrical Transport Properties ◽  
Continuous Transition ◽  
Quantum Critical

The easily tuned balance among competing interactions in Kondo-lattice metals allows access to a zero-temperature, continuous transition between magnetically ordered and disordered phases, a quantum-critical point (QCP). Indeed, these highly correlated electron materials are prototypes for discovering and exploring quantum-critical states. Theoretical models proposed to account for the strange thermodynamic and electrical transport properties that emerge around the QCP of a Kondo lattice assume the presence of an indefinitely large number of itinerant charge carriers. Here, we report a systematic transport and thermodynamic investigation of the Kondo-lattice system CeNi2−δAs2 (δ ≈ 0.28) as its antiferromagnetic order is tuned by pressure and magnetic field to zero-temperature boundaries. These experiments show that the very small but finite carrier density of ∼0.032 e−/formular unit in CeNi2−δAs2 leads to unexpected transport signatures of quantum criticality and the delayed development of a fully coherent Kondo-lattice state with decreasing temperature. The small carrier density and associated semimetallicity of this Kondo-lattice material favor an unconventional, local-moment type of quantum criticality and raises the specter of the Nozières exhaustion idea that an insufficient number of conduction-electron spins to separately screen local moments requires collective Kondo screening.

scholarly journals Quantum criticality in a layered iridate

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Kousik Samanta ◽  
Jean C. Souza ◽  
Danilo Rigitano ◽  
Adimir I. Morales ◽  
Pascoal G. Pagliuso ◽  
...  
Keyword(s):  
Quantum Phase Transitions ◽  
Quantum Critical Point ◽  
Quantum Phase ◽  
Structural Quality ◽  
Linear Temperature Dependence ◽  
Spin Orbital ◽  
Metal Insulator ◽  
Linear Temperature ◽  
Critical Fluctuations ◽  
Quantum Critical

AbstractIridates provide a fertile ground to investigate correlated electrons in the presence of strong spin-orbit coupling. Bringing these systems to the proximity of a metal-insulator quantum phase transition is a challenge that must be met to access quantum critical fluctuations with charge and spin-orbital degrees of freedom. Here, electrical transport and Raman scattering measurements provide evidence that a metal-insulator quantum critical point is effectively reached in 5% Co-doped Sr2IrO4 with high structural quality. The dc-electrical conductivity shows a linear temperature dependence that is successfully captured by a model involving a Co acceptor level at the Fermi energy that becomes gradually populated at finite temperatures, creating thermally-activated holes in the Jeff = 1/2 lower Hubbard band. The so-formed quantum critical fluctuations are exceptionally heavy and the resulting electronic continuum couples with an optical phonon at all temperatures. The magnetic order and pseudospin-phonon coupling are preserved under the Co doping. This work brings quantum phase transitions, iridates and heavy-fermion physics to the same arena.

scholarly journals Giant isotropic magneto-thermal conductivity of metallic spin liquid candidate Pr2Ir2O7 with quantum criticality

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
J. M. Ni ◽  
Y. Y. Huang ◽  
E. J. Cheng ◽  
Y. J. Yu ◽  
B. L. Pan ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Critical Point ◽  
Quantum Critical Point ◽  
Magnetic Monopoles ◽  
Quantum Criticality ◽  
Quantum Spin ◽  
Spin Liquid ◽  
Zero Field ◽  
Spin Liquids ◽  
Quantum Critical

AbstractSpin liquids are exotic states with no spontaneous symmetry breaking down to zero-temperature because of the highly entangled and fluctuating spins in frustrated systems. Exotic excitations like magnetic monopoles, visons, and photons may emerge from quantum spin ice states, a special kind of spin liquids in pyrochlore lattices. These materials usually are insulators, with an exception of the pyrochlore iridate Pr2Ir2O7, which was proposed as a metallic spin liquid located at a zero-field quantum critical point. Here we report the ultralow-temperature thermal conductivity measurements on Pr2Ir2O7. The Wiedemann–Franz law is verified at high fields and inferred at zero field, suggesting no breakdown of Landau quasiparticles at the quantum critical point, and the absence of mobile fermionic excitations. This result puts strong constraints on the description of the quantum criticality in Pr2Ir2O7. Unexpectedly, although the specific heats are anisotropic with respect to magnetic field directions, the thermal conductivities display the giant but isotropic response. This indicates that quadrupolar interactions and quantum fluctuations are important, which will help determine the true ground state of this material.

QUANTUM CRITICAL FLUCTUATIONS IN HEAVY FERMION COMPOUNDS

2002 ◽  
Vol 16 (20n22) ◽  
pp. 3031-3036 ◽  
Author(s):  
A. SCHROEDER ◽  
G. AEPPLI ◽  
P. COLEMAN ◽  
R. RAMAZASHVILI ◽  
R. COLDEA ◽  
...  
Keyword(s):  
Neutron Scattering ◽  
Heavy Fermion ◽  
Magnetic Moments ◽  
Quantum Critical Point ◽  
Electron System ◽  
Spin Fluctuations ◽  
Scattering Data ◽  
Critical Fluctuations ◽  
Conventional View ◽  
Quantum Critical

The electronic properties of heavy fermion alloys are dominated by spin fluctuations which are expected to become critical when tuned by pressure to a quantum critical point (QCP), entering a magnetic ordered state. Apart from the onset of exotic superconductivity, unexpected "normal conducting" behavior is found close to the QCP, which does not seem only to escape the conventional view of metals (Fermi liquids) but also the "conventional view" of an antiferromagnetic quantum phase transition in these f-metals. So far only few compounds have been investigated by neutron scattering to directly reveal the critical fluctuations spectrum. In CeCu 59 Au 01 the fluctuations develop an unusual energy dependence, characterized by an exponent α = 0.75, which persist over the entire Brillouin zone, provoking an unexpected local non Fermi liquid behavior. The same unusual exponent derived from E/T scaling determines the H/T scaling of the uniform magnetization. Recent neutron scattering data in magnetic fields further confirm this picture of nearly free local magnetic moments (modified by α) emerging at the antiferromagnetic QCP in this strongly correlated electron system.

scholarly journals Itinerant quantum critical point with fermion pockets and hotspots

2019 ◽  
Vol 116 (34) ◽  
pp. 16760-16767 ◽  
Author(s):  
Zi Hong Liu ◽  
Gaopei Pan ◽  
Xiao Yan Xu ◽  
Kai Sun ◽  
Zi Yang Meng
Keyword(s):  
Critical Point ◽  
Quantum Monte Carlo ◽  
Fermi Liquid ◽  
Large Scale ◽  
Quantum Critical Point ◽  
Quantum Criticality ◽  
Spin Fluctuations ◽  
Square Lattice ◽  
Quantum Critical ◽  
Antiferromagnetic Spin

Metallic quantum criticality is among the central themes in the understanding of correlated electronic systems, and converging results between analytical and numerical approaches are still under review. In this work, we develop a state-of-the-art large-scale quantum Monte Carlo simulation technique and systematically investigate the itinerant quantum critical point on a 2D square lattice with antiferromagnetic spin fluctuations at wavevector Q=(π,π)—a problem that resembles the Fermi surface setup and low-energy antiferromagnetic fluctuations in high-Tc cuprates and other critical metals, which might be relevant to their non–Fermi-liquid behaviors. System sizes of 60×60×320 (L×L×Lτ) are comfortably accessed, and the quantum critical scaling behaviors are revealed with unprecedented high precision. We found that the antiferromagnetic spin fluctuations introduce effective interactions among fermions and the fermions in return render the bare bosonic critical point into a different universality, different from both the bare Ising universality class and the Hertz–Mills–Moriya RPA prediction. At the quantum critical point, a finite anomalous dimension η∼0.125 is observed in the bosonic propagator, and fermions at hotspots evolve into a non-Fermi liquid. In the antiferromagnetically ordered metallic phase, fermion pockets are observed as the energy gap opens up at the hotspots. These results bridge the recent theoretical and numerical developments in metallic quantum criticality and can serve as the stepping stone toward final understanding of the 2D correlated fermions interacting with gapless critical excitations.

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