Superconductivity in graphene-based systems has recently attracted much attention, as either intr... more Superconductivity in graphene-based systems has recently attracted much attention, as either intrinsic behavior or induced by proximity to a superconductor may lead to interesting topological phases and symmetries of the pairing function. A prominent system considers the pairing to have chiral symmetry. The question arises as to the effect of possible spin–orbit coupling on the resulting superconducting quasiparticle (QP) spectrum. Utilizing a Bogolyubov–de Gennes (BdG) Hamiltonian, we explore the interplay of different interaction terms in the system, and their role in generating complex Berry curvatures in the QP spectrum, as well as non-trivial topological behavior. We demonstrate that the topology of the BdG Hamiltonian in these systems may result in the appearance of edge states along the zigzag edges of nanoribbons in the appropriate regime. For suitable chemical potential and superconducting pairing strength, we find the appearance of robust midgap states at zigzag edges, wel...
We study the Ruderman-Kittel-Kasuya-Yosida interaction between two magnetic impurities connected ... more We study the Ruderman-Kittel-Kasuya-Yosida interaction between two magnetic impurities connected to the edges of zigzag-terminated transition-metal dichalcogenide triangular flakes. When the impurities lie on the edges of the flake, the effective exchange configuration is helical, showing a sizable noncollinear Dzyaloshinskii-Moriya interaction. We analyze the interaction decay exponent for doping levels inside the band gap of the infinite layer, corresponding to edge states for the flake. The exponents show a sub-2D behavior for different band fillings, with a decay that is slower than quadratic. Remarkably, the noncollinear component can feature positive exponents, signaling an interaction that grows with the impurity separation. This effect can be attributed to the presence of an envelope with a wavelength longer than the size of the flake.
Charge density waves and negative differential resistance are seemingly unconnected physical phen... more Charge density waves and negative differential resistance are seemingly unconnected physical phenomena but they coexist after a voltage pulse manipulation on TaS2 surface with an STM tip.
Synthetic molecular machines designed to operate on materials surfaces can convert energy into mo... more Synthetic molecular machines designed to operate on materials surfaces can convert energy into motion and they may be useful to incorporate into solid state devices. Here, we develop and characterize a multi-component molecular propeller that enables unidirectional rotations on a material surface when energized. Our propeller is composed of a rotator with three molecular blades linked via a ruthenium atom to a ratchet-shaped molecular gear. Upon adsorption on a gold crystal surface, the two dimensional nature of the surface breaks the symmetry and left or right tilting of the molecular gear-teeth induces chirality. The molecular gear dictates the rotational direction of the propellers and step-wise rotations can be induced by applying an electric field or using inelastic tunneling electrons from a scanning tunneling microscope tip. By means of scanning tunneling microscope manipulation and imaging, the rotation steps of individual molecular propellers are directly visualized, which ...
Superconductivity in graphene-based systems has recently attracted much attention, as either intr... more Superconductivity in graphene-based systems has recently attracted much attention, as either intrinsic behavior or induced by proximity to a superconductor may lead to interesting topological phases and symmetries of the pairing function. A prominent system considers the pairing to have chiral symmetry. The question arises as to the effect of possible spin–orbit coupling on the resulting superconducting quasiparticle (QP) spectrum. Utilizing a Bogolyubov–de Gennes (BdG) Hamiltonian, we explore the interplay of different interaction terms in the system, and their role in generating complex Berry curvatures in the QP spectrum, as well as non-trivial topological behavior. We demonstrate that the topology of the BdG Hamiltonian in these systems may result in the appearance of edge states along the zigzag edges of nanoribbons in the appropriate regime. For suitable chemical potential and superconducting pairing strength, we find the appearance of robust midgap states at zigzag edges, wel...
We study the Ruderman-Kittel-Kasuya-Yosida interaction between two magnetic impurities connected ... more We study the Ruderman-Kittel-Kasuya-Yosida interaction between two magnetic impurities connected to the edges of zigzag-terminated transition-metal dichalcogenide triangular flakes. When the impurities lie on the edges of the flake, the effective exchange configuration is helical, showing a sizable noncollinear Dzyaloshinskii-Moriya interaction. We analyze the interaction decay exponent for doping levels inside the band gap of the infinite layer, corresponding to edge states for the flake. The exponents show a sub-2D behavior for different band fillings, with a decay that is slower than quadratic. Remarkably, the noncollinear component can feature positive exponents, signaling an interaction that grows with the impurity separation. This effect can be attributed to the presence of an envelope with a wavelength longer than the size of the flake.
Charge density waves and negative differential resistance are seemingly unconnected physical phen... more Charge density waves and negative differential resistance are seemingly unconnected physical phenomena but they coexist after a voltage pulse manipulation on TaS2 surface with an STM tip.
Synthetic molecular machines designed to operate on materials surfaces can convert energy into mo... more Synthetic molecular machines designed to operate on materials surfaces can convert energy into motion and they may be useful to incorporate into solid state devices. Here, we develop and characterize a multi-component molecular propeller that enables unidirectional rotations on a material surface when energized. Our propeller is composed of a rotator with three molecular blades linked via a ruthenium atom to a ratchet-shaped molecular gear. Upon adsorption on a gold crystal surface, the two dimensional nature of the surface breaks the symmetry and left or right tilting of the molecular gear-teeth induces chirality. The molecular gear dictates the rotational direction of the propellers and step-wise rotations can be induced by applying an electric field or using inelastic tunneling electrons from a scanning tunneling microscope tip. By means of scanning tunneling microscope manipulation and imaging, the rotation steps of individual molecular propellers are directly visualized, which ...
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Papers by Sergio Ulloa