Many-body effects on the capacitance of multilayers made from strongly correlated materials

S. T. F. Hale; J. K. Freericks

doi:10.1103/physrevb.85.205444

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

npj Quantum Materials ◽

10.1038/s41535-021-00333-6 ◽

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.

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

Science Advances ◽

10.1126/sciadv.abd6147 ◽

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.

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Ultrafast coupled charge and spin dynamics in strongly correlated NiO

Nature Communications ◽

10.1038/s41467-020-17925-8 ◽

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.

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