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2The observation of chirality is ubiquitous in nature. Contrary to intuition, the population of opposite chiralities is surprisingly asymmetric at fundamental levels [1,2]. Examples range from parity violation in the subatomic weak force [1] to the homochirality in essential biomolecules [2]. The ability to achieve chiralityselective synthesis (chiral induction) is of great importance in stereochemistry, molecular biology and pharmacology [2]. In condensed matter physics, a crystalline electronic system is geometrically chiral when it lacks any mirror plane, space inversion center or roto-inversion axis [3]. Typically, the geometrical chirality is predefined by a material's chiral lattice structure, which is fixed upon the formation of the crystal. 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. We report the realization of optical chiral induction and the observation of a gyrotropically ordered phase in the transition-metal dichalcogenide semimetal 1T -TiSe 2 . We show that shining mid-infrared circularly polarized light near the critical temperature leads to the preferential formation of one chiral domain. As a result, we are able to observe an out-of-plane circular photogalvanic current, whose direction depends on the optical induction. Our study provides compelling evidence for the spontaneous emergence of chirality in the correlated semimetal TiSe 2 [18]. Such chiral induction provides a new way of optical control over novel orders in quantum materials.In the presence of strong correlations, the behavior of electrons in a metal can signficantly deviate from a weakly-interacting Fermi gas, forming a wide range of complex, broken symmetry phases [19]. Recent theoretical works have highlighted their analogy with classical liquids [19], where a rich set of liquid crystalline phases that exhibit varying degrees of symmetry breaking and transport properties have been observed. A well-studied case is the nematic order [19][20][21], i.e., the spontaneous emergence of rotational anisotropy. In classical liquids, this is known as the nematic liquid crystal, whereas in quantum materials, it has recently been observed in quantum Hall systems, ruthenates, high temperature supercon-3 ductors [19], heavy-fermion superconductors [20], and correlated metallic pyrochlores [21].Another fascinating case is the gyrotropic order, i.e., the spontaneous emergence of geometrical chirality. In classical liquids, this is known as the cholesteric liquid crystal. In quantum materials, despite fundamental interest [4][5][6][7][8][9][10][11][12][13][14][15][16], a clear ...

When the Fermi level matches the Dirac point in graphene, the reduced charge screening can dramatically enhance electron-electron (e-e) scattering to produce a strongly interacting Dirac liquid 1-3 . While the dominance of e-e scattering already leads to novel behaviors, such as electron hydrodynamic flow 4, 5 , further exotic phenomena have been predicted to arise specifically from the unique kinematics of e-e scattering in massless Dirac systems 6-11 . Here, we use optoelectronic probes, which are highly sensitive to the kinematics of electron scattering 12-20 , to uncover a giant intrinsic photocurrent response in pristine graphene. This photocurrent emerges exclusively at the charge neutrality point and vanishes abruptly at non-zero charge densities. Moreover, it is observed at places with broken reflection symmetry, and it is selectively enhanced at free graphene edges with sharp bends. Our findings reveal that the photocurrent relaxation is strongly suppressed by a drastic change of fast photocarrier kinematics in graphene when its Fermi level matches the Dirac point. The emergence of robust photocurrents in neutral Dirac materials promises new energy-harvesting functionalities and highlights intriguing electron dynamics in the optoelectronic response of Dirac fluids.Graphene is a model two-dimensional Dirac material with highly tunable transport and optical properties. In particular, it exhibits multiple gate-tunable photocurrent (PC) effects, including the thermoelectric PC driven by an electron temperature gradient [14][15][16]20 and the photovoltaic PC

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Sample suspension is a valuable method to improve the mechanical, thermal, electronic, and optical properties of low-dimensional materials. In terms of confined light-matter waves—the polaritons, sample suspension can elongate the wavelength of polaritons with a positive phase velocity. Previous work demonstrates a wavelength elongation of ∼10% for hyperbolic phonon polaritons (HPPs) in uniaxial crystals of hexagonal boron nitride (hBN). In this work, we report the alteration of HPPs in biaxial α-phase molybdenum trioxide (α-MoO3) by sample suspension. Our combined infrared nano-imaging experiments and electromagnetic theory reveal a wavelength elongation > 60% and a propagation length increase > 140%, due to the simultaneous wavelength elongation and dissipation elimination in the suspended specimen. We have also examined HPPs in α-MoO3 with a negative phase velocity. The sample suspension shortens the HPP wavelength and simultaneously reduces the dissipation due to the unique permittivity tensor. The HPPs with improved figures of merits in the suspended specimen may be developed for nano-polaritonic circuits, biochemical sensing, emission engineering, and energy transfer.