Shovon Pal


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Pal

First Name

Shovon

ORCID

0000-0002-1222-9852

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2017 - 201982020 - 202515
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Publications 1 - 10 of 23
  • Fermi Volume Evolution and Crystal-Field Excitations in Heavy-Fermion Compounds Probed by Time-Domain Terahertz Spectroscopy
    Item type: Journal Article
    Pal, Shovon; Wetli, Christoph; Zamani, F.; et al. (2019)
    Physical Review Letters
  • Two-dimensional spectroscopy on a THz quantum cascade structure
    Item type: Book Chapter
    Markmann, Sergej; Franckié, Martin; Pal, Shovon; et al. (2021)
    Frontiers in Optics and Photonics
    Understanding and controlling the nonlinear optical properties and coherent quantum evolution of complex multilevel systems out of equilibrium is essential for the new semiconductor device generation. In this work, we investigate the nonlinear system properties of an unbiased quantum cascade structure by performing two-dimensional THz spectroscopy. We study the time-resolved coherent quantum evolution after it is driven far from equilibrium by strong THz pulses and demonstrate the existence of multiple nonlinear signals originating from the engineered subbands and find the lifetimes of those states to be in the order of 4-8 ps. Moreover, we observe a coherent population exchange among the first four inter-subband levels during the relaxation, which have been confirmed with our simulation. We model the experimental results with a time-resolved density matrix based on the master equation in Lindblad form, including both coherent and incoherent transitions between all density matrix elements. This allows us to replicate qualitatively the experimental observations and provides access to their microscopic origin.
  • Time-resolved 2D THz-Spectroscopy on a THz quantum cascade structure
    Item type: Conference Paper
    Markmann, Sergej; Franckié, Martin; Pal, Shovon; et al. (2021)
    2021 Conference on Lasers and Electro-Optics (CLEO)
    We have performed two-dimensional THz spectroscopy on an unbiased quantum cascade structure (QCS), and observe multiple nonlinear pump-probe signals originating from the engineered intersubband system. Moreover, we provide experimental and simulation evidence for coherent population transport.
  • Magnetoelectric Phase Control at Domain-Wall-Like Epitaxial Oxide Multilayers
    Item type: Journal Article
    Gradauskaite, Elzbieta; Yang, Chia-Jung; Efe, Ipek; et al. (2025)
    Advanced Functional Materials
    Ferroelectric domain walls are nanoscale objects that can be created, positioned, and erased on demand. They often embody functional properties that are distinct from the surrounding bulk material. Enhanced conductivity, for instance, is observed at charged ferroelectric domain walls. Regrettably, domain walls of this type are scarce because of the energetically unfavorable electrostatics. This hinders the current technological development of domain-wall nanoelectronics. Here this constraint is overcome by creating robust domain-wall-like objects in epitaxial oxide heterostructures. Charged head-to-head (HH) and tail-to-tail (TT) junctions are designed with two ferroelectric layers (BaTiO3 and BiFeO3) that have opposing out-of-plane polarization. To test domain-wall-like functionalities, an ultrathin ferromagnetic La0.7Sr0.3MnO3 layer is inserted into the junctions. The interfacial electron or hole accumulation at the interfaces, set by the HH and TT polarization configurations, respectively, controls the LSMO conductivity and magnetization. Thus it is proposed that trilayers reminiscent of artificial domain walls provide magnetoelectric functionality and may constitute an important building block in the design of oxide-based electronic devices.
  • Two-dimensional coherent spectroscopy of a THz quantum cascade laser: Observation of multiple harmonics
    Item type: Journal Article
    Markmann, Sergej; Nong, Hanond; Pal, Shovon; et al. (2017)
    Optics Express
  • Origin of Terahertz Soft-Mode Nonlinearities in Ferroelectric Perovskites
    Item type: Journal Article
    Pal, Shovon; Strkalj, Nives; Yang, Chia-Jung; et al. (2021)
    Physical Review X
    Soft modes are intimately linked to structural instabilities and are key for the understanding of phase transitions. The soft modes in ferroelectrics, for example, map directly the polar order parameter of a crystal lattice. Driving these modes into the nonlinear, frequency-changing regime with intense terahertz (THz) light fields is an efficient way to alter the lattice and, with it, the physical properties. However, recent studies show that the THz electric-field amplitudes triggering a nonlinear soft-mode response are surprisingly low, which raises the question on the microscopic picture behind the origin of this nonlinear response. Here, we use linear and two-dimensional terahertz (2D THz) spectroscopy to unravel the origin of the soft-mode nonlinearities in a strain-engineered epitaxial ferroelectric SrTiO3 thin film. We find that the linear dielectric function of this mode is quantitatively incompatible with pure ionic or pure electronic motions. Instead, 2D THz spectroscopy reveals a pronounced coupling of electronic and ionic-displacement dipoles. Hence, the soft mode is a hybrid mode of lattice (ionic) motions and electronic interband transitions. We confirm this conclusion with model calculations based on a simplified pseudopotential concept of the electronic band structure. It reveals that the entire THz nonlinearity is caused by the off-resonant nonlinear response of the electronic interband transitions of the lattice-electronic hybrid mode. With this work, we provide fundamental insights into the microscopic processes that govern the softness that any material assumes near a ferroic phase transition. This knowledge will allow us to gain an efficient all-optical control over the associated large nonlinear effects.
  • Two-dimensional spectroscopy on a THz quantum cascade structure
    Item type: Journal Article
    Markmann, Sergej; Franckié, Martin; Pal, Shovon; et al. (2021)
    Nanophotonics
    Understanding and controlling the nonlinear optical properties and coherent quantum evolution of complex multilevel systems out of equilibrium is essential for the new semiconductor device generation. In this work, we investigate the nonlinear system properties of an unbiased quantum cascade structure by performing two-dimensional THz spectroscopy. We study the time-resolved coherent quantum evolution after it is driven far from equilibrium by strong THz pulses and demonstrate the existence of multiple nonlinear signals originating from the engineered subbands and find the lifetimes of those states to be in the order of 4–8 ps. Moreover, we observe a coherent population exchange among the first four intersubband levels during the relaxation, which have been confirmed with our simulation. We model the experimental results with a time-resolved density matrix based on the master equation in Lindblad form, including both coherent and incoherent transitions between all density matrix elements. This allows us to replicate qualitatively the experimental observations and provides access to their microscopic origin.
  • Time-resolved 2D THz-Spectroscopy on a THz quantum cascade structure
    Item type: Other Conference Item
    Markmann, Sergej; Franckié, Martin; Pal, Shovon; et al. (2021)
    OSA Technical Digest ~ Conference on Lasers and Electro-Optics
    We have performed two-dimensional THz spectroscopy on an unbiased quantum cascade structure (QCS), and observe multiple nonlinear pump-probe signals originating from the engineered intersubband system. Moreover, we provide experimental and simulation evidence for coherent population transport.
  • Depolarizing-Field Effects in Epitaxial Capacitor Heterostructures
    Item type: Journal Article
    Strkalj, Nives; De Luca, Gabriele; Campanini, Marco; et al. (2019)
    Physical Review Letters
Publications 1 - 10 of 23