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  • 1.
    Sadhukhan, Banasree
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Bergman, Anders
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Kvashnin, Yaroslav O.
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Hellsvik, Johan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Centra, Parallelldatorcentrum, PDC. NORDITA, Hannes Alfvens Vag 12, SE-10691 Stockholm, Sweden.;Stockholm Univ, Hannes Alfvens Vag 12, SE-10691 Stockholm, Sweden..
    Delin, Anna
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Spin-lattice couplings in two-dimensional CrI3 from first-principles computations2022Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 105, nr 10, artikkel-id 104418Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Since thermal fluctuations become more important as dimensions shrink, it is expected that low-dimensional magnets are more sensitive to atomic displacement and phonons than bulk systems are. Here we present a fully relativistic first-principles study on the spin-lattice coupling, i.e., how the magnetic interactions depend on atomic displacement, of the prototypical two-dimensional ferromagnet CrI3. We extract an effective measure of the spin-lattice coupling in CrI3, which is up to ten times larger than what is found for bcc Fe. The magnetic exchange interactions, including Heisenberg and relativistic Dzyaloshinskii-Moriya interactions, are sensitive both to the in-plane motion of Cr atoms and out-of-plane motion of ligand atoms. We find that significant magnetic pair interactions change sign from ferromagnetic (FM) to antiferromagnetic (AFM) for atomic displacements larger than 0.16 (0.18) angstrom for Cr (I) atoms. We explain the observed strong spin-lattice coupling by analyzing the orbital decomposition of isotropic exchange interactions, involving different crystal-field-split Cr-3d orbitals. The competition between the AFM t(2g)-t(2g) and FM t(2g)-e(g) contributions depends on the bond angle formed by Cr and I atoms as well as Cr-Cr distance. In particular, if a Cr atom is displaced, the FM-AFM sign changes when the I-Cr-I bond angle approaches 90 degrees. The obtained spin-lattice coupling constants, along with the microscopic orbital analysis, can act as a guiding principle for further studies of the thermodynamic properties and combined magnon-phonon excitations in two-dimensional magnets.

  • 2.
    Sadhukhan, Banasree
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik. Presidency Univ, Dept Phys, 86-1 Coll St, Kolkata 700073, India..
    Chimata, Raghuveer
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Sanyal, Biplab
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Mookerjee, Abhijit
    SN Bose Natl Ctr Basic Sci, JD 3, Kolkata 700098, India..
    Magnetization Dynamics in FexCo1-x in Presence of Chemical Disorder2023Inngår i: MAGNETOCHEMISTRY, ISSN 2312-7481, Vol. 9, nr 2, s. 44-, artikkel-id 44Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we present a theoretical formulation of magnetization dynamics in disordered binary alloys, based on the Kubo linear response theory, interfaced with a seamless combination of three approaches: density functional-based tight-binding linear muffin-tin orbitals, generalized recursion and augmented space formalism. We applied this method to study the magnetization dynamics in chemically disordered FexCo1-x (x = 0.2, 0.5, 0.8) alloys. We found that the magnon energies decreased with an increase in Co concentration. Significant magnon softening was observed in Fe20Co80 at the Brillouin zone boundary. Magnon-electron scattering increased with increasing Co content, which in turn modified the hybridization between the Fe and Co atoms. This reduced the exchange energy between the atoms and softened down the magnon energy. The lowest magnon lifetime was found in Fe50Co50, where disorder was at a maximum. This clearly indicated that the damping of magnon energies in FexCo1-x was governed by hybridization between Fe and Co, whereas the magnon lifetime was controlled by disorder configuration. Our atomistic spin dynamics simulations show reasonable agreement with our theoretical approach in magnon dispersion for different alloy compositions.

  • 3.
    Sadhukhan, Banasree
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik. KTH, Skolan för bioteknologi (BIO), Centra, Albanova VinnExcellence Center for Protein Technology, ProNova. Leibniz Inst Solid State & Mat Res IFW Dresden, Helmholtzstr 20, D-01069 Dresden, Germany..
    Nag, Tanay
    Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden.;Rhein Westfal TH Aachen, Inst Theorie Stat Phys, D-52056 Aachen, Germany..
    Effect of chirality imbalance on Hall transport of PrRhC22023Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 107, nr 8, artikkel-id L081110Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Much has been learned about the topological transport in real materials. We investigate the interplay between magnetism and topology in the magnetotransport of PrRhC2. The fourfold degeneracy reduces to twofold followed by nondegenerate Weyl nodes when the orientation of the magnetic quantization axis is changed from easy axis to body diagonal through face diagonal. This engenders chirality imbalance between positive and negative chirality Weyl nodes around the Fermi energy. We observe a significant enhancement in the chiral anomaly mediated response such as planar Hall conductivity and longitudinal magnetoconductivity, due to the emergence of chirality imbalance upon orienting the magnetic quantization axis to body diagonal. The angular variations of the above quantities for different magnetic quantization axes clearly refer to the typical signature of planar Hall effect in Weyl semimetals. We further investigate the profiles of anomalous Hall conductivities as a function of Fermi energy to explore the effects of symmetries as well as chirality imbalance on Berry curvature.

  • 4.
    Sadhukhan, Banasree
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik. IFW Dresden, Leibniz Inst Solid State & Mat Res, Helmholtzstr 20, D-01069 Dresden, Germany..
    Nag, Tanay
    Rhein Westfal TH Aachen, Inst Theorie Stat Phys, D-52056 Aachen, Germany..
    Electronic structure and unconventional nonlinear response in double Weyl semimetal SrSi22021Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 104, nr 24, artikkel-id 245122Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Considering a noncentrosymmetric, nonmagnetic double Weyl semimetal (WSM) SrSi2, we investigate the electron and hole pockets in bulk Fermi surface behavior that enables us to characterize the material as a type-I WSM. We study the structural handedness of the material and correlate it with the distinct surface Fermi surface at two opposite surfaces following an energy evolution. The Fermi arc singlet becomes doublet with the onset of spin orbit coupling that is in accordance with the topological charge of the Weyl nodes (WNs). A finite energy separation between WNs of opposite chirality in SrSi2 allows us to compute circular photogalvanic effect (CPGE). Followed by the three band formula, we show that CPGE is only quantized for Fermi level chosen in the vicinity of WN residing at a higher value of energy. Surprisingly, for the other WN of opposite chirality in the lower value of energy, CPGE is not found to be quantized. Such a behavior of CPGE is in complete contrast to the time reversal breaking WSM where CPGE is quantized to two opposite plateau depending on the topological charge of the activated WN. We further analyze our finding by examining the momentum resolved CPGE. Finally we show that two band formula for CPGE is not able to capture the quantization that is apprehended by the three band formula.

  • 5.
    Sadhukhan, Banasree
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Nag, Tanay
    SISSA, Via Bonomea 265, I-34136 Trieste, Italy..
    Role of time reversal symmetry and tilting in circular photogalvanic responses2021Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 103, nr 14, artikkel-id 144308Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study the role of time reversal symmetry (TRS) in the circular photogalvanic (CPG) responses considering a chiral Weyl semimetal (WSM), while a quantized CPG response is guaranteed by both the broken inversion symmetry and broken mirror symmetries. The TRS broken WSM yields one left and one right chiral Weyl node (WN), while there are two left and right chiral WNs for a TRS invariant WSM. We show that these features can potentially cause the quantization of a CPG response at higher values compared to the topological charge of the underlying WSM. This is further supported by the fact that Berry curvature and velocity behave differently depending on whether the system preserves or breaks the TRS. We find the CPG responses for a TRS invariant type-II WSM to be quantized at two and four times the topological charge of the activated WNs while the chemical potentials are, respectively, chosen in the vicinity of the energies associated with the left and right chiral WNs. By contrast, irrespective of the above choice of the chemical potential, the quantization in the CPG response is directly given by the topological charge of the activated WNs for the TRS broken case. Interestingly, we notice a nonquantized peak in the CPG response when the energies of the WNs associated with opposite chiralities are close to each other, as is the case for the TRS invariant type-I WSM considered here. Moreover, we show that the tilt can significantly modify the CPG response as the velocity in the tilt direction changes, which enters into the CPG tensor through the Fermi distribution function. Given these exciting outcomes, the second-order CPG response emerges as a useful indicator to characterize the system under consideration. Furthermore, we investigate the momentum resolved structure of the CPG response to relate with the final results and strengthen our analysis from the perspective of the lattice models.

  • 6.
    Sadhukhan, Surasree
    et al.
    Indian Inst Technol Goa, Sch Phys Sci, Ponda 403401, India..
    Sadhukhan, Banasree
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik. IFW Dresden, Inst Theoret Solid State Phys, Helmholtz str 20, D-01069 Dresden, Germany..
    Kanungo, Sudipta
    Indian Inst Technol Goa, Sch Phys Sci, Ponda 403401, India..
    Pressure-driven tunable properties of the small-gap chalcopyrite topological quantum material ZnGeSb2: A first-principles study2022Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 106, nr 12, artikkel-id 125112Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Search for new topological quantum materials is the demand of time and the theoretical prediction plays a crucial role besides the obvious experimental verification. Divination of topological properties in already well-known narrow gap semiconductors is a flourishing area in quantum material. In this view we revisited the semiconductor compound in the chalcopyrite series, with a very small gap near the Fermi energy. Using the density functional theory-based first-principles calculations, we report a strong topologically nontrivial phase in chalcopyrite ZnGeSb2, which can act as a model system of strained HgTe. The calculations reveal the nonzero topological invariant (Z2), the presence of Dirac cone crossing in the surface spectral functions with spin-momentum locked spin texture. We also study the interplay between the structural parameters and electronic properties, and report the tunable topological properties due to a very small band gap, from nontrivial to trivial phase under the application of moderate hydrostatic pressure within approximate to 7 GPa. A small modification of a lattice parameter is enough to achieve this topological phase transition which is easily accomplished in an experimental laboratory. The calculations show that a discontinuity in the tetragonal distortion of noncentrosymmetric ZnGeSb2 plays a crucial role in driving this topological phase transition. Our results are further collaborated with a low energy k center dot p model Hamiltonian to validate our abinitio findings. We showed that the evaluation of the model band energy dispersion under the hydrostatic pressure is consistent with the obtained results.

1 - 6 of 6
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