| graphene | |
|---|---|
| Name | Graphene |
| Appearance | Monolayer of sp2 carbon atoms |
| Discovered | 2004 |
| Discoverers | Andre Geim and Konstantin Novoselov |
| First isolation | Mechanical exfoliation |
| Applications | Quantum sensor, semiconductor device, photonic device |
graphene
Graphene is a single layer of carbon atoms arranged in a two-dimensional honeycomb lattice and represents the prototypical two-dimensional material. Its low-energy excitations behave as massless relativistic quasiparticles, making graphene an important platform in Quantum Physics for studying relativistic-like quantum mechanics, topological phenomena, and quantum transport in condensed matter. The coexistence of high carrier mobility, tunable carrier density and strong quantum effects at accessible temperatures has driven intense research across physics, materials science, and electrical engineering.
Graphene's lattice symmetry and linear band crossing at the Brillouin zone corners give rise to emergent quasiparticles described by a two-dimensional Dirac equation, establishing a bridge between condensed matter and relativistic quantum field theory. Its discovery by Andre Geim and Konstantin Novoselov at the University of Manchester led to experimental demonstrations of phenomena analogous to relativistic effects, prompting the 2010 Nobel Prize in Physics. Because of reduced dimensionality and weak screening, graphene exhibits enhanced electron–electron correlations and quantum interference effects that make it an ideal testbed for phenomena such as Klein tunneling, quantum Hall physics, and many-body instabilities investigated in institutions like Columbia University and Max Planck Institute for Solid State Research.
At low energies the π and π* bands touch at six K points, with the two inequivalent points labeled K and K'. Near these points the electronic dispersion is linear, E(k) ≈ ħv_F|k|, where v_F ≈ 10^6 m/s is the Fermi velocity. Low-energy excitations are commonly modeled as two-component spinors obeying a massless Dirac Hamiltonian, leading to the notion of "Dirac fermions" in graphene. The description employs concepts from band theory, tight-binding model and continuum field theories; seminal theoretical treatments include works by Philip R. Wallace and later developments within the Dirac cone framework. Sublattice (pseudospin) and valley degrees of freedom (K, K') act like internal quantum numbers, underpinning proposals for valleytronics and valley-dependent quantum control.
Graphene's quantum transport displays distinctive signatures: a minimal conductivity near the charge neutrality point, suppressed backscattering due to pseudospin chirality, and an anomalous integer quantum Hall effect with half-integer plateaus first observed by K. S. Novoselov and collaborators. In high magnetic fields and low temperatures graphene exhibits both integer and fractional quantum Hall states; fractional states indicate strong electron correlation and were measured in high-mobility samples produced by encapsulation with hexagonal boron nitride grown by groups such as at University of Manchester and Columbia University. Mesoscopic transport experiments probe weak localization and universal conductance fluctuations, while superconducting proximity experiments yield specular Andreev reflection and gate-tunable Josephson junctions investigated by teams at Harvard University and University of Basel.
Electron–phonon coupling in graphene is unusually weak for in-plane modes but strongly dependent on doping and substrate interaction. Optical phonons at the Γ and K points produce prominent signatures in Raman spectroscopy, notably the G and 2D peaks exploited by experimentalists at Raman spectroscopy facilities and companies like Graphenea for material characterization. Weak electron–phonon scattering contributes to long phase coherence lengths and high thermal conductivity, relevant for quantum interference and decoherence in graphene-based qubits and interferometers. Coupling to out-of-plane flexural modes and to substrates such as SiO2 or encapsulants like hexagonal boron nitride modifies scattering rates and influences many-body phenomena including superconducting correlations reported in twisted graphene systems.
Patterning graphene into nanoribbons, quantum dots and constrictions produces quantum confinement and discrete energy spectra; electronic structure depends sensitively on edge termination (zigzag vs armchair). Zigzag edges support localized edge states with flat-band features and enhanced local magnetism predicted by density functional theory and observed in scanning tunnelling microscopy studies at institutions such as IBM Research and Max Planck Institute for Microstructure Physics. Graphene nanoribbons synthesized via bottom-up chemical routes (e.g., work from Columbia University and Institute for Basic Science) realize tunable bandgaps, enabling transistor-like behavior and spin-polarized edge modes relevant to quantum information proposals. Twist-stacked bilayers produce moiré superlattices and emergent flat bands; notably, twisted bilayer graphene near the “magic angle” exhibits correlated insulator states and unconventional superconductivity that intersect condensed-matter quantum many-body research.
Graphene's combination of coherence, tunability, and surface sensitivity supports applications in quantum technologies and sensors. Graphene-based quantum Hall resistance standard devices exploit robust quantization for metrology in laboratories such as National Institute of Standards and Technology and the National Physical Laboratory (UK). Proposals for graphene qubits, spin qubits, and valley qubits leverage long spin coherence and gate control; hybrid devices combine graphene with superconductors (e.g., Aluminium contacts) to create Andreev qubits and topological superconducting platforms. Graphene's high carrier mobility and low noise also enable ultrasensitive magnetometer and chemical sensor architectures, while integrated photonic and plasmonic devices explore single-photon detection and quantum optoelectronics in collaborations between MIT and industrial partners.
Category:Carbon allotropes Category:Two-dimensional materials Category:Condensed matter physics