arXiv subjects

Amar Bharti

Publications and source records attributed to Amar Bharti.

9 recordsLinked to original sources

arXiv2026

Helicity-engineered nonlinear optical responses in photo-excited topological semimetals

Topological materials provide a transformative arena for light-driven control of electronic motion; yet, direct manipulation of electron dynamics on sub-cycle timescale remains a significant challenge. We demonstrate that the strong-field-driven high-harmonic generation of a Weyl semimetal can be controlled and manipulated through bicircular pump-probe driving fields. While a lone probe pulse generates exclusively odd-order harmonics, the addition of a pump pulse triggers a series of sidebands arising from nonlinear frequency mixing of pump and probe photons. Our results reveal that the sideband intensities are highly sensitive to the relative helicity of the pulses and the orientation of the polarization plane. This sensitivity stems from the chiral nature of the Weyl nodes, which couples efficiently to the light's helicity only when the node-separation axis is perpendicular to the polarization plane. Furthermore, the significant suppression of sideband intensity with increasing pump-probe delay identifies these features as a potential clock for electron-hole decoherence. These findings establish frequency-mixed high-harmonic generation as a sensitive probe of chiral quantum dynamics and suggest a robust framework for manipulating topological currents via structured light, with implications for lightwave electronics and ultrafast quantum information processing.

physics.optics↗

arXiv2026

Coherent control of chirality in Weyl semimetals

Weyl fermions in inversion-symmetric Weyl semimetals occur in pairs of opposite chirality, leading to symmetric optical responses under circularly-polarised light and a vanishing net photocurrent. Here, we show that tailored two-colour light fields break this symmetry and enable selective excitation of individual Weyl nodes. The interference between a circularly-polarised $ω$ field and a phase-locked linearly-polarised $2ω$ field generates a chirality-dependent redistribution of carriers in momentum space, resulting in a nonzero controllable photocurrent. We demonstrate that both the magnitude and sign of the photocurrent can be tuned via the relative phase and field strength of the two colours, and identify an optimal regime in which chiral selectivity is maximised. Our results establish a general route to optically-controlled chiral charge dynamics in Weyl semimetals using polarisation-structured light.

cond-mat.mes-hall↗

arXiv2025

Nonlinear Optical Spectroscopy of Nodal-Line Semimetals

Intense laser-driven nonlinear optical phenomena in two-dimensional (2D) nodal-line semimetals (NLS) exhibit complex mechanisms, particularly in the NbSi$_{x}$Te$_{2}$ material systems characterized by nonsymmorphic symmetry-protected band degeneracy. Our findings reveal how nonsymmorphic symmetry-protected band degeneracy fundamentally influences the material's nonlienar optical responses. Notably, the nonsymmorphic glide-mirror symmetry leads to the exclusive generation of odd-order harmonics from inversion-symmetry-broken NLS. Moreover, harmonics are emitted parallel and perpendicular to the driving laser's polarization. We demonstrate distinct generation mechanisms arise from intrachain and interchain processes, with their relative contributions varying significantly with the polarization of the driving laser pulse. The polarization-dependence exhibits two-fold anisotropy, with each harmonic order showing characteristic angular distributions of maximum yield. Additionally, our analysis of the ellipticity-dependence reveals an intricate interplay between interband and intraband mechanisms. These insights open new possibilities for controlling harmonic generation through precise tuning parameters of the driving laser and highlight the potentials of NLS materials to fabricate lightwave-based photonics, optoelectronic and quantum devices operating on ultrafast timescales.

physics.optics↗

arXiv2025

Intense Laser-Driven Phenomena In Weyl Semimetals

Condensed-matter provides attractive platforms to realize exotic particles, originally proposed in high-energy physics. Weyl semimetal (WSM) is a material in which low-energy collective excitations are governed by massless Weyl fermions, which appear in pairs of opposite chirality and are topologically protected. Thus, the discovery of topological materials such as WSM has heralded a new era in contemporary physics. Moreover, these materials offer exciting opportunities in next-generation signal processing and optoelectronics. This thesis explores different facets of the intense laser-driven phenomena in WSM for applications in emerging lightwave-driven Petahertz electronics and quantum technologies.

cond-mat.mes-hall↗

arXiv2024

Photocurrent generation in solids via linearly polarized laser

To add to the rapidly progressing field of ultrafast photocurrent, we propose a universal method to generate photocurrent in normal and topological materials using a pair of multicycle linearly polarized laser pulses. The interplay of the fundamental and its second harmonic pulses is studied for the generation of photocurrent in Weyl semimetals by varying the angle between the polarization direction, relative intensity, and relative phase delay. It has been found that the presence of a comparatively weaker second harmonic pulse is sufficient to generate substantial photocurrent. Moreover, significant photocurrent is generated even when polarization directions are orthogonal for certain ratios of the lasers' intensities. In addition, the photocurrent is found to be susceptible to the delay between the two pulses. We have illustrated that all our findings are extendable to non-topological and two-dimensional materials, such as graphene and molybdenum disulfide.

cond-mat.mes-hall↗

arXiv2023

Tailoring Photocurrent in Weyl Semimetals via Intense Laser Irradiation

Generating and tailoring photocurrent in topological materials has immense importance in fundamental studies and the technological front. Present work introduces a universal method to generate ultrafast photocurrent in {\it both} inversion-symmetric and inversion-broken Weyl semimetals with degenerate Weyl nodes at the Fermi level. Our approach harnesses the asymmetric electronic population in the conduction band induced by an intense {\it single-color} circularly polarized laser pulse. It has been found that the induced photocurrent can be tailored by manipulating helicity and ellipticity of the employed laser. Moreover, our approach generates photocurrent in realistic situations when the Weyl nodes are positioned at different energies and have finite tilt along a certain direction. Present work adds a new dimension on practical applications of Weyl semimetals for optoelectronics and photonics-based quantum technologies.

physics.optics↗

arXiv2023

How massless are Weyl fermions in Weyl semimetals?

Circularly polarized light fails to generate currents in inversion-symmetric Weyl semimetals with degenerate Weyl nodes. While each node generates current with the direction depending on its chirality, the two currents in the two degenerate nodes of opposite chirality cancel each other. By extension, it is also generally expected that the currents generated at the same Weyl node by the fields of opposite helicity should also observe mirror symmetry and cancel. Surprisingly, here we find that this is not the case. The origin of this effect lies in the nonlinear energy dispersion, which manifests strongly already very close to the Weyl nodes, where linear dispersion is expected to hold and the Weyl fermions are thus expected to be massless. A scheme based on using a trefoil field composed of a counterrotating fundamental and its second harmonic is proposed to control the induced asymmetry at a chiral node from positive to negative, including zero.

cond-mat.str-el↗

arXiv2023

Role of topological charges in the nonlinear-optical response from Weyl semimetals

The successful realization of the topological Weyl semimetals has revolutionized contemporary physics. In recent years, multi-Weyl semimetals, a class of topological Weyl semimetals, has attracted broad interest in condensed-matter physics. Multi-Weyl semimetals are emerging topological semimetals with nonlinear anisotropic energy dispersion, which is characterized by higher topological charges. In this study, we investigate how the topological charge affects the nonlinear optical response from multi-Weyl semimetals. It has been observed that the laser-driven electronic current is characteristic of the topological charge, and the laser polarization's direction influences the current's direction and amplitude. In addition, the anomalous current, perpendicular to the laser's polarization, carries a distinct signature of the topological charges and encodes the information about the parity and amplitude of the nontrivial Berry curvature. We show that the anomalous current associated with the anomalous Hall effect remains no longer proportional to the topological charge at higher laser intensity -- a significant deviation from the linear response theory. High-harmonic spectroscopy is employed to capture the distinct and interesting features of the currents in multi-Weyl semimetals where the topological charge drastically impacts the harmonics' yield and energy cutoff.

cond-mat.str-el↗

arXiv2022

High-harmonic spectroscopy of light-driven nonlinear anisotropic anomalous Hall effect in a Weyl semimetal

Weyl semimetals are promising quantum materials that offer unique topological properties. Lately, it has been shown that laser-driven electron dynamics have characteristic signatures in two-dimensional and three-dimensional Dirac semimetals. The transition from Dirac to Weyl semimetal requires the breaking of either inversion or time-reversal symmetry. The present work shows that the laser-driven electron dynamics in a Weyl semimetal with broken time-reversal symmetry has intriguing features in its high-harmonic spectrum. It is found that the parity and magnitude of the non-zero Berry curvature's components control the direction and strength of the anomalous current, which leads to the generation of the anomalous odd harmonics. We demonstrate that the non-trivial topology of the Berry curvature in time-reversal symmetry broken quantum materials can be probed by measuring the polarisation of the emitted anomalous odd harmonics. Our findings unequivocally illustrate that laser-driven electron dynamics leads to the generation of nonlinear anisotropic anomalous Hall effect in time-reversal symmetry broken quantum materials on an ultrafast timescale.

cond-mat.mes-hall↗