Spinor spherical harmonics

Not to be confused with Spin-weighted spherical harmonics.

In quantum mechanics, the spinor spherical harmonics ^[1] (also known as spin spherical harmonics, ^[2] spinor harmonics ^[3] and Pauli spinors ^[4] ) are special functions defined over the sphere. The spinor spherical harmonics are the natural spinor analog of the vector spherical harmonics. While the standard spherical harmonics are a basis for the angular momentum operator, the spinor spherical harmonics are a basis for the total angular momentum operator (angular momentum plus spin). These functions are used in analytical solutions to Dirac equation in a radial potential. ^[3] The spinor spherical harmonics are sometimes called Pauli central field spinors, in honor of Wolfgang Pauli who employed them in the solution of the hydrogen atom with spin–orbit interaction. ^[1]

Properties

The spinor spherical harmonics Y_{l, s, j, m} are the spinors eigenstates of the total angular momentum operator squared:

${\displaystyle {\begin{aligned}\mathbf {j} ^{2}Y_{l,s,j,m}&=j(j+1)Y_{l,s,j,m}\\\mathrm {j} _{\mathrm {z} }Y_{l,s,j,m}&=mY_{l,s,j,m}\;;\;m=-j,-(j-1),\cdots ,j-1,j\\\mathbf {l} ^{2}Y_{l,s,j,m}&=l(l+1)Y_{l,s,j,m}\\\mathbf {s} ^{2}Y_{l,s,j,m}&=s(s+1)Y_{l,s,j,m}\end{aligned}}}$

where j = l + s, where j, l, and s are the (dimensionless) total, orbital and spin angular momentum operators, j is the total azimuthal quantum number and m is the total magnetic quantum number.

Under a parity operation, we have

${\displaystyle PY_{l,sj,m}=(-1)^{l}Y_{l,s,j,m}.}$

For spin-1/2 systems, they are given in matrix form by ^{[1] [3] [5]}

${\displaystyle Y_{l,\pm {\frac {1}{2}},j,m}={\frac {1}{\sqrt {2{\bigl (}j\mp {\frac {1}{2}}{\bigr )}+1}}}{\begin{pmatrix}\pm {\sqrt {j\mp {\frac {1}{2}}\pm m+{\frac {1}{2}}}}Y_{l}^{m-{\frac {1}{2}}}\\{\sqrt {j\mp {\frac {1}{2}}\mp m+{\frac {1}{2}}}}Y_{l}^{m+{\frac {1}{2}}}\end{pmatrix}}.}$

where ${\displaystyle Y_{l}^{m}}$ are the usual spherical harmonics.

References

1. Biedenharn, L. C.; Louck, J. D. (1981), Angular momentum in Quantum Physics: Theory and Application, Encyclopedia of Mathematics, vol. 8, Reading: Addison-Wesley, p. 283, ISBN   0-201-13507-8
2. Edmonds, A. R. (1957), Angular Momentum in Quantum Mechanics , Princeton University Press, ISBN   978-0-691-07912-7
3. Greiner, Walter (6 December 2012). "9.3 Separation of the Variables for the Dirac Equation with Central Potential (minimally coupled)". Relativistic Quantum Mechanics: Wave Equations. Springer. ISBN   978-3-642-88082-7.
4. Rose, M. E. (2013-12-20). Elementary Theory of Angular Momentum. Dover Publications, Incorporated. ISBN   978-0-486-78879-1.
5. Berestetskii, V. B.; E. M. Lifshitz; L. P. Pitaevskii (2008). Quantum electrodynamics. Translated by J. B. Sykes; J. S. Bell (2nd ed.). Oxford: Butterworth-Heinemann. ISBN   978-0-08-050346-2. OCLC   785780331.