Electrical Tuning of the Excitonic Insulator Ground State of 
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi>Ta</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi>NiSe</mml:mi></mml:mrow><mml:mrow><mml:mn>5</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:mrow></mml:math>

Fukutani, Keisuke; Stania, Roland; Schwier, Eike F.; Shimada, Kenya; Kwon, Chang Il; Yeom, Han Woong

doi:10.1103/physrevlett.123.206401

Cited by 47 publications

(24 citation statements)

References 42 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…At T c , the valence band maximum measured by ARPES at continuously shifts to higher binding energy up to about 0.18 eV [6,7], and the optical band gap increases in a similar way up to about 0.16 to 0.22 eV [8,9]. The nature of the low-energy electronic structure above T c is currently heavily debated and argued to be a semimetal [10][11][12], a zero-gap semiconductor [13], or a semiconductor [6,7,14]. The difficulty of classifying its electronic structure arises from the small size of the band gap at the Fermi level and the occurrence of fluctuations of the low-temperature phase [7], potentially hiding the true semimetallic nature of Ta 2 NiSe 5 [16].…”

Section: Introductionmentioning

confidence: 99%

Mapping the unoccupied state dispersions in Ta2NiSe5 with resonant inelastic x-ray scattering

et al. 2020

View full text Add to dashboard Cite

The transition metal chalcogenide Ta 2 NiSe 5 undergoes a second-order phase transition at T c = 328 K involving a small lattice distortion. Below T c , a band gap at the center of its Brillouin zone increases up to about 0.35 eV. In this work, we study the electronic structure of Ta 2 NiSe 5 in its low-temperature semiconducting phase, using resonant inelastic x-ray scattering (RIXS) at the Ni L 3 edge. In addition to a weak fluorescence response, we observe a collection of intense Raman-like peaks that we attribute to electron-hole excitations. Using density functional theory calculations of its electronic band structure, we identify the main Raman-like peaks as interband transitions between valence and conduction bands. By performing angle-dependent RIXS measurements, we uncover the dispersion of these electron-hole excitations that allows us to extract the low-energy boundary of the electron-hole continuum. From the dispersion of the valence band measured by angle-resolved photoemission spectroscopy, we derive the effective mass of the lowest unoccupied conduction band.

show abstract

Section: Introductionmentioning

confidence: 99%

Mapping the unoccupied state dispersions in Ta2NiSe5 with resonant inelastic x-ray scattering

et al. 2020

View full text Add to dashboard Cite

show abstract

“…Second, at low temperatures we no longer observe any bands overlapping and there is only a single band dispersion within 0.3 eV of µ in the occupied states. That state exhibits a characteristic "M" shaped dispersion 13,17,20,33,34 , which becomes sharper as the temperature is further lowered (Fig. 2(c,f)).…”

mentioning

confidence: 95%

“…Transport and optical spectroscopy indicate a near-zero band gap at high temperatures but the opening of a band gap at low temperatures 12,18 , with a clear resistivity anomaly at T c =327 K 19 . Previous low-temperature angle-resolved photoemission (ARPES) measurements show an anomalous flattened dispersion of the valence band maximum, indicating that it is a hybridised ground state 13,20 , while a number of time-resolved studies have found evidence for a fast timescale associated with electronic interactions 13,14 . Nev-ertheless, there is also a non-negligible coupling to the lattice.…”

mentioning

confidence: 97%

Band hybridization at the semimetal-semiconductor transition of Ta2NiSe5 enabled by mirror-symmetry breaking

Watson

Marković

Morales

et al. 2020

Phys. Rev. Research

View full text Add to dashboard Cite

We present a combined study from angle-resolved photoemission and density-functional theory calculations of the temperature-dependent electronic structure in the excitonic insulator candidate Ta2NiSe5. Our experimental measurements unambiguously establish the normal state as a semimetal with a significant band overlap of >100 meV. Our temperature-dependent measurements indicate how these low-energy states hybridise when cooling through the well-known 327 K phase transition in this system. From our calculations and polarisationdependent photoemission measurements, we demonstrate the importance of a loss of mirror symmetry in enabling the band hybridisation, driven by a shear-like structural distortion which reduces the crystal symmetry from orthorhombic to monoclinic. Our results thus point to the key role of the lattice distortion in enabling the phase transition of Ta2NiSe5.

show abstract

“…In stark contrast, there have been growing but debated experimental evidences [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] of excitons formed spontaneously without any external excitation or artificial structures to constitute an insulating ground state with a finite number of steady-state excitons [33][34][35] . Such an excitonic insulator (EI) is one fundamental manybody insulating state of solids, which was theoretically proposed as early as 1960's for a small gap semiconductor or a semimetal [33][34][35] .…”

mentioning

confidence: 99%

Detecting photoelectrons from spontaneously formed excitons

et al. 2021

Self Cite

View full text Add to dashboard Cite

Excitons, quasiparticles of electrons and holes bound by Coulombic attraction, are created transiently by light and play an important role in optoelectronics, photovoltaics and photosynthesis. While they are also predicted to form spontaneously in a small gap semiconductor or a semimetal, leading to a Bose-Einstein condensate at low temperature, their material realization has been elusive without any direct evidence. Here we detect the direct photoemission signal from spontaneously formed excitons in a debated excitonic insulator candidate Ta2NiSe5. Our symmetry-selective angle-resolved photoemission spectroscopy reveals a characteristic excitonic feature above the transition temperature, which provides detailed properties of excitons such as anisotropic Bohr radius. The present result evidences so called preformed excitons and guarantees the exciton insulator nature of Ta2NiSe5 at low temperature. Direct photoemission can be an important tool to characterize steady-state excitons.

show abstract

Electrical Tuning of the Excitonic Insulator Ground State of Ta2NiSe5

Cited by 47 publications

References 42 publications

Mapping the unoccupied state dispersions in Ta2NiSe5 with resonant inelastic x-ray scattering

Mapping the unoccupied state dispersions in Ta2NiSe5 with resonant inelastic x-ray scattering

Band hybridization at the semimetal-semiconductor transition of Ta2NiSe5 enabled by mirror-symmetry breaking

Detecting photoelectrons from spontaneously formed excitons

Contact Info

Product

Resources

About