We investigate, for the first time, the thermal signature of a single-stranded helical molecule that is described beyond usual nearest-neighbor electron hopping, by analyzing electronic specific heat. Depending on the hopping of electrons, two different kinds of helical systems are considered. In one case the hopping is confined within a few neighboring lattice sites which is referred to as short-range hopping helix, while in the other case, electrons can hop in all possible sites making the system a long-range hopping one. These two helices accurately emulate the structures of single-stranded DNA and protein molecules, respectively. Each helix geometry is exposed to a transverse electric field applied perpendicular to the helix axis. The interplay among the helicity, higher-order hopping, and the electric field has significant impact on thermal response. Our comprehensive theoretical analysis reveals that, under low-temperature conditions, the short-range hopping helix exhibits greater sensitivity to temperature compared to the long-range hopping helix system. Conversely, the scenario reverses in the high-temperature limit. The thermal response of the helices can be modified selectively by means of the electric field, and the difference between the specific heats of the two helices gradually decreases with increasing the field strength. The molecular handedness, on the other hand, does not have any appreciable effect on the thermal signature. In addition, we also explore a significant application of electronic specific heat (ESH). Finally, we discuss the results of ESH by considering the spin degree of freedom and in the context of real biological helical systems.
We illustrate possible topological phases in honeycomb lattice with textures in electron hopping energy between nearest-neighboring sites and show that they are characterized by the mirror winding number intimately related to the chiral (or sublattice) symmetry. Analytic wave functions of zero-energy edge modes in ribbon geometry are provided, which are classified into even and odd sectors with respect to the mirror operation with the mirror plane perpendicular to the edge, and evolve into the topological helical edge states at finite momenta. Intriguingly our results demonstrate that in order…
We study Aharonov-Bohm effect in a two-terminal helical ring with long-range hopping in presence of Rashba spin-orbit interaction. We explore how the spin polarization behavior changes depending on the applied magnetic flux and the incoming electron energy. The most interesting feature that we articulate in this system is that zero-energy crossings appear in the energy spectra at $Φ=0$ and also at integer multiples of half-flux quantum values ($n Φ_0/2$, $n$ being an integer) of the applied magnetic flux. We investigate the transport properties of the ring using Green's function formalism and …
Recent studies indicated that helical organic molecules, such as DNA and $α$-helical protein, can behave as Thouless quantum pumps when a rotating electric field is applied perpendicularly to their helical axes. Here we investigate the influence of long-range hoppings on this topological pumping of electrons in single-helical organic molecules. Under variation of the long-range hoppings governed by a decay exponent $μ$, we find an energy gap in the molecular band structure closes at a critical value $μ_c$ of the decay exponent and reopens for $μ$ deviating from $μ_c$. The relevant bulk bands i…
For two-dimensional lattices in a tight-binding description, the intrinsic spin-orbit coupling, acting as a complex next-nearest-neighbor hopping, opens gaps that exhibit the quantum spin Hall effect. In this paper, we study the effect of a real next-nearest-neighbor hopping term on the band structure of several Dirac systems. In our model, the spin is conserved, which allows us to analyze the spin Chern numbers. We show that in the Lieb, kagome, and T_3 lattices, variation of the amplitude of the real next-nearest-neighbor hopping term drives interesting topological phase transitions. These t…
We formulate the necessary and sufficient conditions for the existence of dispersionless energy eigenvalues (so-called `flat bands') and their associated compact localized eigenstates in $M$-dimensional tight-binding lattices with $N$ sites per unit cell and complex-amplitude nearest-neighbour tunneling between the lattice sites. The degrees of freedom $M$ can be traded for longer-range complex hopping in lattices with reduced dimensionality. We show the conditions explicitly for $(M = 1, N\leq4)$, $(M = 2, N = 2,3)$, and $(M = 3, N = 2,3)$, and outline their systematic construction for arbitr…
Conformational effect on electronic localization is critically investigated for the first time considering a double-stranded helical geometry (DSHG) subjected to an electric field. In the presence of electric field the DSHG behaves like a correlated disordered system whose site potentials are modulated in a cosine form like the well known Aubry-Andre-Harper (AAH) model. The potential distribution can be modulated further by changing the orientation of the incident field. A similar kind of cosine modulation is also introduced in the inter-strand hopping integrals of the DSHG. Suitably adjusting…
The integration of diverse electronic phenomena, such as magnetism and nontrivial topology, into a single system is normally studied either by seeking materials that contain both ingredients, or by layered growth of contrasting materials. The ability to simply stack very different two dimensional (2D) van der Waals materials in intimate contact permits a different approach. Here we use this approach to couple the helical edges states in a 2D topological insulator, monolayer WTe2, to a 2D layered antiferromagnet, CrI3. We find that the edge conductance is sensitive to the magnetization state of…
Accurate determination of electron-hole asymmetry and next-nearest neighbor hopping in graphene
次近邻跳跃项t'决定了石墨烯中几种现象的大小和重要性，这些现象包括由于断裂的键引起的自掺杂和在t'存在下不再完美的克莱因隧穿。理论估计的t'变化很大，而一些现有的测量，通过使用偏振分辨磁谱已经发现了令人惊讶的大t'，接近或甚至超过最高的理论值。在这里，我们报告了通过使用高质量电容设备对石墨烯中的态密度进行的专门测量。态密度表现出明显的电子-空穴不对称性，随能量线性增加。该行为产生约-0.30 eV +-15%的t'，与理论估计的高端一致。我们讨论了电子-电子相互作用在确定t'和概述的现象，可以影响这样一个大的值的t'的作用。
In typical flat-band models, defined as nearest-neighbor tight-binding models, flat bands are usually pinned to the special energies, such as top or bottom of dispersive bands, or band-crossing points. In this paper, we propose a simple method to tune the energy of flat bands without losing the exact flatness of the bands. The main idea is to add farther-neighbor hoppings to the original nearest-neighbor models, in such a way that the transfer integral depends only on the Manhattan distance. We apply this method to several lattice models including the two-dimensional kagome lattice and the thr…
We investigate corner states in a photonic two-dimensional (2D) Su-Schrieffer-Heeger (SSH) model on a square lattice with zero gauge flux. By considering intracelluar next-nearest-neighbor (NNN) hoppings, we discover a broad class of corner states in the 2D SSH model, and show that they are robust against certain fabrication disorders. Moreover, these corner states are located around the corners, but not at the corner points, so we refer to them as general corner states. We analytically identify that the general corner states are induced by the intracelluar NNN hoppings (long-range interaction…
Helical conductors with spin-momentum locking are promising platforms for Majorana fermions. Here we report observation of two topologically distinct phases supporting helical edge states in charge neutral Bernal-stacked tetralayer graphene in Hall bar and Corbino geometries. As the magnetic field B and out-of-plane displacement field D are varied, we observe a phase diagram consisting of an insulating phase and two metallic phases, with 0, 1 and 2 helical edge states, respectively. These phases are accounted for by a theoretical model that relates their conductance to spin-polarization platea…
We investigate the existence and stability of skyrmions in a frustrated chiral ferromagnet by considering the competition between ferromagnetic (FM) nearest-neighbour (NN) interaction ($J_1$) and antiferromagnetic (AFM) next-nearest-neighbour (NNN) interaction ($J_2$). Contrary to the general wisdom that long-range ferromagnetic order is not energy preferable under frustration, the skyrmion lattice not only exists but is even stable for a large field range when $J_2 \leq J_1$ compared with frustration-free systems. We defend that the enlargement of stability window of skyrmions is a consequenc…
Energy-Selective Complete Spin Polarization in an Extended Su-Schrieffer-Heeger Ferromagnetic Chain
School of Physical Sciences, National Institute of Science Education and Research（国家科学教育与研究中心物理科学学院）；Homi Bhabha National Institute（霍米·巴巴国立研究所）；Institute of Physics, Sachivalaya Marg（萨奇瓦亚拉 marg 物理研究所）
Electrostatic Screening Modulation of Graphene's Electronic Structure and the Helical Wavefunction Dominated Topological Properties
Key Laboratory of Extraordinary Bond Engineering and Advanced Materials Technology (EBEAM) of Chongqing, College of Mechanical and Electrical Engineering, Yangtze Normal University（重庆极端键合工程与先进材料技术重点实验室，长江师范学院机电工程学院）
We report the realization of a synthetic magnetic field for photons and polaritons in a honeycomb lattice of coupled semiconductor micropillars. A strong synthetic field is induced in both the s and p orbital bands by engineering a uniaxial hopping gradient in the lattice, giving rise to the formation of Landau levels at the Dirac points. We provide direct evidence of the sublattice symmetry breaking of the lowest-order Landau level wavefunction, a distinctive feature of synthetic magnetic fields. Our realization implements helical edge states in the gap between n=0 and n=1 Landau levels, expe…
