scholarly journals Imaging the coherent propagation of collective modes in the excitonic insulator Ta2NiSe5 at room temperature

2021 ◽  
Vol 7 (28) ◽  
pp. eabd6147
Author(s):  
Hope M. Bretscher ◽  
Paolo Andrich ◽  
Yuta Murakami ◽  
Denis Golež ◽  
Benjamin Remez ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Substantial Contribution ◽  
Collective Modes ◽  
Strongly Correlated ◽  
Many Body ◽  
Phonon Modes ◽  
Pump Probe ◽  
Strongly Correlated Materials ◽  
Excitonic Insulator ◽  
Micrometer Scale

Excitonic insulators host a condensate of electron-hole pairs at equilibrium, giving rise to collective many-body effects. Although several materials have emerged as excitonic insulator candidates, evidence of long-range coherence is lacking and the origin of the ordered phase in these systems remains controversial. Here, using ultrafast pump-probe microscopy, we investigate the possible excitonic insulator Ta2NiSe5. Below 328 K, we observe the anomalous micrometer-scale propagation of coherent modes at velocities of ~105 m/s, which we attribute to the hybridization between phonon modes and the phase mode of the condensate. We develop a theoretical framework to support this explanation and propose that electronic interactions provide a substantial contribution to the ordered phase in Ta2NiSe5. These results allow us to understand how the condensate’s collective modes transport energy and interact with other degrees of freedom. Our study provides a unique paradigm for the investigation and manipulation of these properties in strongly correlated materials.

scholarly journals Spin dynamics and Griffiths singularity in the random quantum Ising magnet PrTiNbO6

2021 ◽  
Vol 6 (1) ◽  
Author(s):  
Yuesheng Li ◽  
Qiao-Yi Li ◽  
Wei Li ◽  
Tao Liu ◽  
David J. Voneshen ◽  
...  
Keyword(s):  
Spin Dynamics ◽  
Transverse Field ◽  
Strongly Correlated ◽  
Many Body ◽  
Continuous Spin ◽  
Strongly Correlated Materials ◽  
Ising Spin ◽  
Quantum Phenomena ◽  
Rare Regions ◽  
Ising Magnet

AbstractIn crystalline magnets, interaction randomness is usually thought as a negative factor preventing interesting quantum phenomena to occur. However, intriguing interplay between randomness and quantumness can also leads to unique phenomena in the strongly correlated materials. Among others, the random transverse-field Ising spin chain (RTIC) hosts a renowned quantum Griffiths phase. Although the RTIC model has been regarded as a toy model for long, here we materialize this model with the compound PrTiNbO6, which has a disordered ground state with pronounced quantum fluctuations and continuous spin excitations. The observed anomalous spin dynamics of PrTiNbO6 can be accounted by the RTIC model with a consistent set of parameters determined from fitting the thermodynamic data, and it is ascribed to the quantum Griffiths rare regions in the system. Our results provide a concrete example of quantum Griffiths magnet, and offer an ideal experimental platform for investigating the dynamical properties of random many-body system.

scholarly journals Exciton-driven antiferromagnetic metal in a correlated van der Waals insulator

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Carina A. Belvin ◽  
Edoardo Baldini ◽  
Ilkem Ozge Ozel ◽  
Dan Mao ◽  
Hoi Chun Po ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Van Der Waals ◽  
Metallic State ◽  
Strongly Correlated ◽  
Many Body ◽  
Electron Hole ◽  
Strongly Correlated Electron ◽  
Long Wavelength ◽  
Correlated Electron ◽  
Strongly Correlated Electron Materials

AbstractCollective excitations of bound electron-hole pairs—known as excitons—are ubiquitous in condensed matter, emerging in systems as diverse as band semiconductors, molecular crystals, and proteins. Recently, their existence in strongly correlated electron materials has attracted increasing interest due to the excitons’ unique coupling to spin and orbital degrees of freedom. The non-equilibrium driving of such dressed quasiparticles offers a promising platform for realizing unconventional many-body phenomena and phases beyond thermodynamic equilibrium. Here, we achieve this in the van der Waals correlated insulator NiPS3 by photoexciting its newly discovered spin–orbit-entangled excitons that arise from Zhang-Rice states. By monitoring the time evolution of the terahertz conductivity, we observe the coexistence of itinerant carriers produced by exciton dissociation and a long-wavelength antiferromagnetic magnon that coherently precesses in time. These results demonstrate the emergence of a transient metallic state that preserves long-range antiferromagnetism, a phase that cannot be reached by simply tuning the temperature. More broadly, our findings open an avenue toward the exciton-mediated optical manipulation of magnetism.

scholarly journals Review on quasi-2D square planar nickelates

CrystEngComm ◽  
2021 ◽  
Author(s):  
Junjie Zhang ◽  
Xutang Tao
Keyword(s):  
Physical Properties ◽  
Degrees Of Freedom ◽  
Insulator Transition ◽  
Strongly Correlated ◽  
Metal Insulator Transition ◽  
Metal Insulator ◽  
Strongly Correlated Materials ◽  
Square Planar ◽  
Magnetic Resistance

In strongly correlated materials, lattice, charge, spin and orbital degrees of freedom interact with each other, leading to emergent physical properties such as superconductivity, colossal magnetic resistance and metal-insulator transition....

scholarly journals Ultrafast melting and recovery of collective order in the excitonic insulator Ta2NiSe5

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Hope M. Bretscher ◽  
Paolo Andrich ◽  
Prachi Telang ◽  
Anupam Singh ◽  
Luminita Harnagea ◽  
...  
Keyword(s):  
Ground State ◽  
Room Temperature ◽  
Near Infrared ◽  
Infrared Range ◽  
Many Body ◽  
Phonon Modes ◽  
Equilibrium Dynamics ◽  
Excitonic Insulator ◽  
Optical Signature ◽  
The Status

AbstractThe layered chalcogenide Ta2NiSe5 has been proposed to host an excitonic condensate in its ground state, a phase that could offer a unique platform to study and manipulate many-body states at room temperature. However, identifying the dominant microscopic contribution to the observed spontaneous symmetry breaking remains challenging, perpetuating the debate over the ground state properties. Here, using broadband ultrafast spectroscopy we investigate the out-of-equilibrium dynamics of Ta2NiSe5 and demonstrate that the transient reflectivity in the near-infrared range is connected to the system’s low-energy physics. We track the status of the ordered phase using this optical signature, establishing that high-fluence photoexcitations can suppress this order. From the sub-50 fs quenching timescale and the behaviour of the photoinduced coherent phonon modes, we conclude that electronic correlations provide a decisive contribution to the excitonic order formation. Our results pave the way towards the ultrafast control of an exciton condensate at room temperature.

Study of Collective Modes and Elastic Constants of Zr57Ti5Cu20Ni8Al10 Bulk Metallic Glass

2013 ◽  
Vol 209 ◽  
pp. 62-65
Author(s):  
Brijmohan Y. Thakore ◽  
P.H. Suthar ◽  
Chaudhari Prakruti ◽  
P.N. Gajjar ◽  
A.R. Jani
Keyword(s):  
Metallic Glass ◽  
Bulk Metallic Glass ◽  
Elastic Constants ◽  
Interatomic Potential ◽  
Model Potential ◽  
Collective Modes ◽  
Many Body ◽  
Phonon Modes ◽  
Long Wavelength ◽  
Local Field Correction

The methodical expressions for the phonon frequencies of Zr57Ti5Cu20Ni8Al10 bulk metallic glass (BMG) both for longitudinal and transverse phonon modes are computed for the first time using Hubbard-Beeby (HB) approach and our well recognized model potential. The self-consistent phonon scheme given by Takeno-Goda, involving multiple scattering and phonon Eigen frequencies expressed in terms of many-body correlation functions of atoms as well as of interatomic potential in the solids, has been used to generate the collective modes in the Zr57Ti5Cu20Ni8Al10 BMG. In the present paper, the local field correction functions due to Hartree (H), Farid et al (F), Sarkar et al (S) and Hubbard Sham (HS) are used to examine the influence of screening effects on the vibrational properties. Further, from the long wavelength limit of phonon frequencies, various elastic constants have been calculated and are found to be in good agreement with experimental and other available data.

scholarly journals Sequential localization of a complex electron fluid

2019 ◽  
Vol 116 (36) ◽  
pp. 17701-17706 ◽  
Author(s):  
Valentina Martelli ◽  
Ang Cai ◽  
Emilian M. Nica ◽  
Mathieu Taupin ◽  
Andrey Prokofiev ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Electron Localization ◽  
Strongly Correlated ◽  
Unified Framework ◽  
Spin Orbital ◽  
Single Degree Of Freedom ◽  
Strongly Correlated Materials ◽  
Multiple Degrees Of Freedom ◽  
Energy Behavior ◽  
Correlated Quantum Systems

Complex and correlated quantum systems with promise for new functionality often involve entwined electronic degrees of freedom. In such materials, highly unusual properties emerge and could be the result of electron localization. Here, a cubic heavy fermion metal governed by spins and orbitals is chosen as a model system for this physics. Its properties are found to originate from surprisingly simple low-energy behavior, with 2 distinct localization transitions driven by a single degree of freedom at a time. This result is unexpected, but we are able to understand it by advancing the notion of sequential destruction of an SU(4) spin–orbital-coupled Kondo entanglement. Our results implicate electron localization as a unified framework for strongly correlated materials and suggest ways to exploit multiple degrees of freedom for quantum engineering.

scholarly journals Ultrafast coupled charge and spin dynamics in strongly correlated NiO

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Konrad Gillmeister ◽  
Denis Golež ◽  
Cheng-Tien Chiang ◽  
Nikolaj Bittner ◽  
Yaroslav Pavlyukh ◽  
...  
Keyword(s):  
Band Gap ◽  
Spin Dynamics ◽  
Strongly Correlated ◽  
Many Body ◽  
Electronic Band ◽  
Time Resolved ◽  
Spin Correlations ◽  
Strongly Correlated Materials ◽  
Electronic Band Gap ◽  
Gap States

Abstract Charge excitations across an electronic band gap play an important role in opto-electronics and light harvesting. In contrast to conventional semiconductors, studies of above-band-gap photoexcitations in strongly correlated materials are still in their infancy. Here we reveal the ultrafast dynamics controlled by Hund’s physics in strongly correlated photoexcited NiO. By combining time-resolved two-photon photoemission experiments with state-of-the-art numerical calculations, an ultrafast (≲10 fs) relaxation due to Hund excitations and related photo-induced in-gap states are identified. Remarkably, the weight of these in-gap states displays long-lived coherent THz oscillations up to 2 ps at low temperature. The frequency of these oscillations corresponds to the strength of the antiferromagnetic superexchange interaction in NiO and their lifetime vanishes slightly above the Néel temperature. Numerical simulations of a two-band t-J model reveal that the THz oscillations originate from the interplay between local many-body excitations and antiferromagnetic spin correlations.

scholarly journals Ultrafast evolution and transient phases of a prototype out-of-equilibrium Mott–Hubbard material

2017 ◽  
Vol 8 (1) ◽  
Author(s):  
G. Lantz ◽  
B. Mansart ◽  
D. Grieger ◽  
D. Boschetto ◽  
N. Nilforoushan ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Lattice Distortion ◽  
Metallic Phase ◽  
Optical Manipulation ◽  
Strongly Correlated ◽  
Optical Pulses ◽  
Strongly Correlated Materials ◽  
Thermal Phase ◽  
New States ◽  
Transient Phases

Abstract The study of photoexcited strongly correlated materials is attracting growing interest since their rich phase diagram often translates into an equally rich out-of-equilibrium behaviour. With femtosecond optical pulses, electronic and lattice degrees of freedom can be transiently decoupled, giving the opportunity of stabilizing new states inaccessible by quasi-adiabatic pathways. Here we show that the prototype Mott–Hubbard material V2O3 presents a transient non-thermal phase developing immediately after ultrafast photoexcitation and lasting few picoseconds. For both the insulating and the metallic phase, the formation of the transient configuration is triggered by the excitation of electrons into the bonding a 1g orbital, and is then stabilized by a lattice distortion characterized by a hardening of the A 1g coherent phonon, in stark contrast with the softening observed upon heating. Our results show the importance of selective electron–lattice interplay for the ultrafast control of material parameters, and are relevant for the optical manipulation of strongly correlated systems.

scholarly journals Correlation between ground state and orbital anisotropy in heavy fermion materials

2015 ◽  
Vol 112 (8) ◽  
pp. 2384-2388 ◽  
Author(s):  
Thomas Willers ◽  
Fabio Strigari ◽  
Zhiwei Hu ◽  
Violetta Sessi ◽  
Nicholas B. Brookes ◽  
...  
Keyword(s):  
Ground State ◽  
Heavy Fermion ◽  
Degrees Of Freedom ◽  
Great Accuracy ◽  
Wave Functions ◽  
Antiferromagnetic Order ◽  
Strongly Correlated ◽  
Strongly Correlated Materials ◽  
Crystal Electric Field ◽  
Heavy Fermion Materials

The interplay of structural, orbital, charge, and spin degrees of freedom is at the heart of many emergent phenomena, including superconductivity. Unraveling the underlying forces of such novel phases is a great challenge because it not only requires understanding each of these degrees of freedom, it also involves accounting for the interplay between them. Cerium-based heavy fermion compounds are an ideal playground for investigating these interdependencies, and we present evidence for a correlation between orbital anisotropy and the ground states in a representative family of materials. We have measured the 4f crystal-electric field ground-state wave functions of the strongly correlated materials CeRh1−xIrxIn5 with great accuracy using linear polarization-dependent soft X-ray absorption spectroscopy. These measurements show that these wave functions correlate with the ground-state properties of the substitution series, which covers long-range antiferromagnetic order, unconventional superconductivity, and coexistence of these two states.

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