Optical gyrotropy and the nonlocal Hall effect in chiral charge-orderedTiSe2

Abstract

This is the final published version of the article (version of record). It first appeared online via APS at http://journals.aps.org/prb/abstract/10.1103/PhysRevB.92.041111. Please refer to any applicable terms of use of the publisher. University of Bristol -Explore Bristol Research General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. It has been suggested that materials which break spatial inversion symmetry, but not time reversal symmetry, will be optically gyrotropic and display a nonlocal Hall effect. The associated optical rotary power and the suggested possibility of inducing a Kerr effect in such materials, in turn, are central to recent discussions about the nature of the pseudogap phases of various cuprate high-temperature superconductors. In this Rapid Communication, we show that optical gyrotropy and the nonlocal Hall effect provide a sensitive probe of broken inversion symmetry in 1T -TiSe 2 . This material was recently found to possess a chiral charge-ordered phase at low temperatures, in which inversion symmetry is spontaneously broken, while time reversal symmetry remains unbroken throughout its phase diagram. We estimate the magnitude of the resulting gyrotropic constant and optical rotary power (the Faraday effect at zero applied field) and suggest that 1T -TiSe 2 may be employed as a model material in the interpretation of measurements on cuprate superconductors. Introduction. The measurement of a Kerr effect in the pseudogap phase of several high-temperature superconductors constrains the symmetries that this state may exhibit [1][2][3][4]. Although the particular experimental setup used in these studies allows for a nonzero linear response to arise under equilibrium conditions only in the presence of broken time reversal symmetry [5][6][7][8][9], it has been argued that the observed optical activity may nonetheless be fundamentally linked to a breakdown of spatial inversion symmetry, related to the presence of charge order [8]. That it is possible for a chargeordered state to spontaneously break inversion symmetry even in the absence of magnetism or electrostatic polarization, has only recently become clear, with the discovery of chiral charge order in the low-temperature phase of 1T -TiSe 2 [10][11][12][13][14][15]. This unexpected emergence of a spiral configuration among the scalar charge density was explained theoretically by the simultaneous presence of orbital order, yielding a vectorial combined order parameter [11,16]. The charge-and orbitalordered state in this scenario must arise through a sequence of phase transitions, as indicated schematically in Fig. 1, and confirmed experimentally by specific heat, transport, and diffraction experiments [15].The chiral charge and orbital order in 1T -TiSe 2 forms an ideal test case for studying the types of phases that have been argued to dominate the optical activity of high-temperature superconductors. It provides an experimentally accessible sett...

Spontaneous gyrotropic electronic order in a transition-metal dichalcogenide

“…By contrast, a particularly unconventional scenario is the gyrotropic order [4][5][6][7][8], where chirality spontaneously emerges across a phase transition as the electron system breaks the relevant symmetries of an originally achiral lattice. Such a gyrotropic order, proposed as the quantum analogue of the cholesteric liquid crystals, has attracted significant interest [4][5][6][7][8][9][10][11][12][13][14][15][16][17]. However, to date, a clear observation and manipulation of the gyrotropic order remain challenging.…”

“…These new physics further call for the unambiguous demonstration and manipulation of the gyrotropic order in quantum materials.One challenge is to identify a clear experimental signature for geometrical chirality in metals. For insulating chiral crystals or molecules, chirality can be measured by optical activity [6,17], which manifests as the rotation of the linear polarization plane as light travels through a nonmagnetic chiral medium. However, this is difficult in metallic bulk materials as they do not transmit light in bulk samples.…”

Elemental chalcogens as a minimal model for combined charge and orbital order

“…In contrast, helices of increased electronic density necessarily require the onset of charge order to be accompanied by a simultaneous onset of orbital order [3,6,7]. Although this restricts the class of materials in which chiral charge order may appear [8], it has nevertheless been theoretically suggested to play an important role in determining material properties of various transition metal dichalcogenides [8][9][10], and even cuprate high-temperature superconductors [11][12][13].…”

Observation of orbital order in the Van der Waals material 1T-TiSe2

“…This is especially striking in the case of 1T -TiSe 2 , whose charge order (CDW) below T CDW 200 K was discovered decades ago [16]. Debates about its nature and driving mechanism, however, are only recently converging towards a combination of exciton formation and lattice effects stabilising a condensate of particle-hole pairs [17][18][19][20][21][22][23][24][25], while debate about its potential chirality continues until the present day [26][27][28][29][30][31]. Within this context, we establish here that additionally, the electronic ground state in 1T -TiSe 2 has a non-trivial orbital structure.…”