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Spontaneous gyrotropic electronic order in a transition-metal dichalcogenide

Abstract

Chirality is ubiquitous in nature, and populations of opposite chiralities are surprisingly asymmetric at fundamental levels1,2. Examples range from parity violation in the subatomic weak force to homochirality in biomolecules. The ability to achieve chirality-selective synthesis (chiral induction) is of great importance in stereochemistry, molecular biology and pharmacology2. In condensed matter physics, a crystalline electronic system is geometrically chiral when it lacks mirror planes, space-inversion centres or rotoinversion axes1. Typically, geometrical chirality is predefined by the chiral lattice structure of a material, which is fixed on formation of the crystal. By contrast, in materials with gyrotropic order3,4,5,6, electrons spontaneously organize themselves to exhibit macroscopic chirality in an originally achiral lattice. Although such order—which has been proposed as the quantum analogue of cholesteric liquid crystals—has attracted considerable interest3,4,5,6,7,8,9,10,11,12,13,14,15, no clear observation or manipulation of gyrotropic order has been achieved so far. Here we report the realization of optical chiral induction and the observation of a gyrotropically ordered phase in the transition-metal dichalcogenide semimetal 1T-TiSe2. We show that shining mid-infrared circularly polarized light on 1T-TiSe2 while cooling it below the critical temperature leads to the preferential formation of one chiral domain. The chirality of this state is confirmed by the measurement of an out-of-plane circular photogalvanic current, the direction of which depends on the optical induction. Although the role of domain walls requires further investigation with local probes, the methodology demonstrated here can be applied to realize and control chiral electronic phases in other quantum materials4,16.

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Fig. 1: Crystal structure and basic characterizations of 1T-TiSe2.
Fig. 2: Observation of an emergent out-of-plane circular photogalvanic current upon chiral induction.
Fig. 3: Dependence of chiral induction and spontaneously emergent gyrotropic order on the temperature and laser power.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request. Some datasets are available at the Materials Data Facility at https://doi.org/10.18126/r4sn-m7sa.

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Acknowledgements

We thank X. Xu, V. Fatemi, E. J. Sie and S. Fang for discussions. N.G., S.-Y.X., A.K. and A.Z. acknowledge support from the US Department of Energy, Office of Science, Office of Basic Energy Sciences, DMSE (data taking and analysis) and the Gordon and Betty Moore Foundation’s EPiQS Initiative through grant GBMF4540 (manuscript writing). Work in P.J.-H. group was supported through AFOSR grant FA9550-16-1-0382 (fabrication and measurement), as well as through the Center for the Advancement of Topological Semimetals, an Energy Frontier Research Center funded by the US Department of Energy Office of Science, Office of Basic Energy Sciences, through the Ames Laboratory under contract DE-AC02-07CH11358 (data analysis), and the Gordon and Betty Moore Foundation’s EPiQS Initiative through grant GBMF 4541 to P.J.-H. This work made use of the Materials Research Science and Engineering Center Shared Experimental Facilities supported by the National Science Foundation (NSF) (grant number DMR-0819762). The work at Drexel University was supported by NSF through grant number ECCS-1711015. Research conducted at CHESS is supported by the NSF via awards DMR-1332208 and DMR-1829070. Work at CMU was supported by the Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division, through grant number DE-SC0012509. K.W. and T.T. acknowledge support from the Elemental Strategy Initiative conducted by MEXT, Japan, JSPS KAKENHI grant numbers JP18K19136 and CREST (JPMJCR15F3), JST. T.-R.C. was supported by the Young Scholar Fellowship Program of the Ministry of Science and Technology (MOST) in Taiwan, under a MOST grant for the Columbus Program MOST108-2636-M-006-002, National Cheng Kung University, Taiwan, and National Center for Theoretical Sciences, Taiwan. This work was supported partially by MOST, Taiwan, via grant MOST107-2627-E-006-001. This research was supported in part by a Higher Education Sprout Project, Ministry of Education from the Headquarters of University Advancement at National Cheng Kung University (NCKU). S.-M.H. acknowledges support by the Ministry of Science and Technology (MoST) in Taiwan under grant number 105-2112-M-110-014-MY3. H.L. acknowledges Academia Sinica, Taiwan for support under Innovative Materials and Analysis Technology Exploration (AS-iMATE-107-11).

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Authors

Contributions

N.G. and P.J.-H. supervised the project. S.-Y.X. and Q.M. conceived the experiment. S.-Y.X. and Q.M. performed photocurrent measurements and analysed the data. A.K., J.P.C.R., S.-Y.X. and Q.M. performed X-ray diffraction measurements. A.M.M.V., T.H.D., Q.M. and S.-Y.X. fabricated the devices. Y.G. and S.-Y.X. performed theoretical analysis under the supervision of D.X. C.-H.H., S.-M.H., B.S. and T.-R.C. performed density functional theory calculations under the supervision of H.L. G.K. grew TiSe2 crystals. K.W. and T.T. grew the bulk h-BN single crystals. A.Z. made significant contributions to the symmetry analysis and the overall presentation. S.-Y.X., Q.M., P.J.-H. and N.G. wrote the manuscript with input from all authors.

Corresponding authors

Correspondence to Pablo Jarillo-Herrero or Nuh Gedik.

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The authors declare no competing interests.

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Peer review information Nature thanks Sajal Dhara, Jasper van Wezel and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data figures and tables

Extended Data Fig. 1 Polarization-independent photocurrent.

Measured photothermoelectric (PTE) current \({{I}}_{{z}}^{{\rm{PTE}}}\) at different temperatures during heating of the sample from 50 K tow room temperature. The data shown here are from the same photocurrent measurements as those in Fig. 2d, h; they represent the polarization-independent component, whereas those in Fig. 2d, h are the polarization-dependent component of the photocurrent. PTE currents of about 10 nA, 40 nA and 150 nA at 250 K, 170 K and 50 K correspond to a temperature increase of about 2 K, 0.5 K and 0.1 K at 50 K, 170 K and 250 K, respectively, according to the thermopower values measured in ref. 46.

Extended Data Fig. 2 Contrasting behaviours of in-plane and out-of-plane photocurrents as a result of the gyrotropic order in 1T-TiSe2.

a, b, Optical image (a) and schematic illustration (b) of a TiSe2 photoactive device that can detect both the in-plane and out-of-plane photocurrents independently. The electrodes are labelled by capital letters. c, Spatial map of the out-of-plane photocurrent Iz between electrodes G–A at T = 100 K. d, Polarization-dependent Iz data at T = 100 K. The measured photocurrent Iz is consistent with the results of previous devices (Figs. 2, 3). A single peak is observed in c that roughly covers the device. This peak consists of two independent signals: the polarization-independent background, which arises from the photothermoelectric effect and exists at all temperatures, and the polarization-dependent CPGE signal (d), which depends on chiral induction and appears only at low temperatures. e–h, Same as c, d, but for the in-plane photocurrent Ix,y between electrodes C–H (e, f) and C–D (g, h). Ix,y shows distinctly different properties from Iz. No in-plane CPGE is observed (f, h). The polarization-independent signal shows a bipolar spatial configuration (e, g): Ix,y changes sign as the beam spot is scanned from one contact to the other. This bipolar spatial configuration, which has been widely observed in other in-plane photocurrent studies23, further confirms that the polarization-independent signals are photothermoelectric currents at the contact–sample junctions. Scale bars, 25 μm. All data in this figure were collected after RCP chiral induction with an induction power of 30 mW.

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Xu, SY., Ma, Q., Gao, Y. et al. Spontaneous gyrotropic electronic order in a transition-metal dichalcogenide. Nature 578, 545–549 (2020). https://doi.org/10.1038/s41586-020-2011-8

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