Table 2 Spin-Laue classification for \({{\rm{AA}}}^{{\prime} }\)-stacked bilayer MnPS3 under parallel (↑↓/↑↓) and antiparallel (↑↓/↓↑) magnetic orderings

From: Engineering altermagnetism via layer shifts and spin order in bilayer MnPS3

Offset/structure

Phase (Zeng et al.)

MSG

Spin-Laue group

Generators/comment

\({{\rm{AA}}}^{{\prime} }\uparrow \downarrow /\uparrow \downarrow\) (Parallel) ordering

(0,0)

AM (Type III/1\({\overline{3}}^{2}m\))

\(P\overline{6}{\prime} {2}^{{\prime} }m\) (189.221)

\(\{[h| | E]:h\in H\}\cup [{C}_{2}| | {C}_{{\rm{spin}}}^{2}]\)

Broken \({\mathcal{P}}{\mathcal{T}}\); \([{C}_{2}| | {C}_{{\rm{spin}}}^{2}]\) connector present.

(0,1/3)

AM (Type III/22/2mx)

\({C}^{{\prime} }m\) (8.32)

\(\{[h| | E]:h\in H\}\cup [{m}_{x}| | {C}_{{\rm{spin}}}^{2}]\)

Broken \({\mathcal{P}}{\mathcal{T}}\); mirror-type connector \([{m}_{x}| | {C}_{{\rm{spin}}}^{2}]\).

(1/3,1/3)

AM (Type III/22/2mx)

\({C}^{{\prime} }m\) (8.32)

\(\{[h| | E]:h\in H\}\cup [{m}_{x}| | {C}_{{\rm{spin}}}^{2}]\)

Broken \({\mathcal{P}}{\mathcal{T}}\); mirror-type connector \([{m}_{x}| | {C}_{{\rm{spin}}}^{2}]\).

(1/3,2/3)

AFM (Type II)

P321 (150)

{[hE]: h H} [PT]

Effective \({\mathcal{P}}{\mathcal{T}}\) via inversion pairing; no splitting.

(1/2,0)

AFM (Type II)

Aem2 (39)

{[hE]: h H} [PT]

\(2{\bf{t}}\in {\mathcal{L}}\) restores an effective \({\mathcal{P}}{\mathcal{T}}\); spin degeneracy observed.

\({{\bf{AA}}}^{{\prime} }\uparrow \downarrow /\downarrow \uparrow\) (Antiparallel) ordering

(0,0)

AM (Type III/1\({\overline{3}}^{2}m\))

\(P\overline{6}{\prime} 2{m}^{{\prime} }\) (189.223)

\(\{[h| | E]:h\in H\}\cup [{C}_{2}| | {C}_{{\rm{spin}}}^{2}]\)

Broken \({\mathcal{P}}{\mathcal{T}}\); \([{C}_{2}| | {C}_{{\rm{spin}}}^{2}]\) connector survives.

(0,1/3)

AM (Type III/22/2mx)

\({C}^{{\prime} }m\) (8.32)

\(\{[h| | E]:h\in H\}\cup [{m}_{x}| | {C}_{{\rm{spin}}}^{2}]\)

Broken \({\mathcal{P}}{\mathcal{T}}\); mirror-type connector \([{m}_{x}| | {C}_{{\rm{spin}}}^{2}]\).

(1/3,1/3)

AM (Type III/22/2mx)

\({C}^{{\prime} }m\) (8.32)

\(\{[h| | E]:h\in H\}\cup [{m}_{x}| | {C}_{{\rm{spin}}}^{2}]\)

Broken \({\mathcal{P}}{\mathcal{T}}\); mirror-type connector \([{m}_{x}| | {C}_{{\rm{spin}}}^{2}]\).

(1/3,2/3)

AM (Type III/1\({\overline{3}}^{2}m\))

\(P321{\prime}\) (150.25)

\(\{[h| | E]:h\in H\}\cup [{C}_{2}| | {C}_{{\rm{spin}}}^{2}]\)

Broken \({\mathcal{P}}{\mathcal{T}}\); \([{C}_{2}| | {C}_{{\rm{spin}}}^{2}]\) connector present.

(1/2,0)

AM (Type III/2m2m1m)

\(A{\prime} e{\prime} m2\) (39.197)

\(\{[h| | E]:h\in H\}\cup [{m}_{x}| | {C}_{{\rm{spin}}}^{2}]\)

Broken \({\mathcal{P}}{\mathcal{T}}\); mirror-type connector with spin inversion yields Type III altermagnetism.

  1. Type II AFM phases possess spin degeneracy via \({\mathcal{P}}{\mathcal{T}}\); Type III altermagnets require surviving non-degeneracy-enforcing connectors of the form \([a| | {C}_{{\rm{spin}}}^{2}]\), with a {P, Mz, C2z}8,9. The restoration of \({\mathcal{P}}{\mathcal{T}}\) in the parallel (1/2, 0) case is described as “effective”, since it originates from the composite stacking operation [Pτz] combined with time reversal6,17.
  2. Parenthetical 2D-AM labels are from Zeng et al.8. The magnetic space groups (MSG) follow the classification in ref. 13.