Band velocity and effective mass
For a wave packet in one smooth band E(k), neglecting anomalous velocity, v=(1/ħ)∇_kE and ħk̇=F.
Key knowledge
For a wave packet in one smooth band E(k), neglecting anomalous velocity, v=(1/ħ)∇_kE and ħk̇=F. Band curvature defines (m*⁻¹)_ij=(1/ħ²)∂²E/(∂k_i∂k_j), so a_i=Σ_j(m*⁻¹)_ijF_j. An isotropic quadratic minimum gives E≈E_c+ħ²|k−k_c|²/(2m*) with positive electron mass; hole excitation mass at a valence maximum is defined from the opposite curvature.
Values and equations
v=(1/ħ)∇_kE; ħk̇=F; (m*⁻¹)_ij=(1/ħ²)∂²E/(∂k_i∂k_j)
- v
- Band packet velocity m s⁻¹
- k
- Crystal wavevector m⁻¹
- E
- Band energy J
- ħ
- Reduced Planck constant J s
- F
- Slow external force N
- m*⁻¹
- Inverse effective-mass tensor kg⁻¹
- i,j
- Cartesian indices
Conditions and scope
- Semiclassical narrow wave packet in an isolated band, force varying slowly on lattice scales, negligible interband tunnelling/scattering during the acceleration step and negligible Berry-curvature contribution.
- Crystal ħk is not generally mechanical momentum. Band extrema can be anisotropic or degenerate; a single isotropic mass need not exist, and the tensor inverse is the curvature definition.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Solid State Physics: third-year lecture notes (2012): §16.1 equations 16.1–16.4 and Effective Mass and Equations of Motion: group velocity and curvature, with anisotropic qualification. The work/energy chain-rule derivation implies ħk̇=F; excludes the printed 1/ħ factor in 16.5 and identification of crystal momentum with universal mechanical momentum.
2026-10-10 · Independent AI editorial review: All 136 unique authored Physics compact statements, all hypotheses and displayed equations/variable/units tables, all 192 Physics-origin semantic links, exact 165 author inspection matrix and mapped retained conceptual claims have been independently read. Three Physics-tagged Measurement realization records are delegated to root Measurement review. Scientific source verification combines exact author section inspection with independent whole compact-content/semantic review and targeted primary rechecks recorded below; it does not claim each full source body was independently reread. Independent AI editorial review is not human specialist certification or experimental replication. Field inventory is approved after independently reviewing the two added source-inspected band-construction methods. Receipt: physics-independent-content-inventory-review.1.
Entry details
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