1. Magnetic WKB constructions;['Bonnaillie-Noël, Virginie', 'Hérau, Frédéric', 'Raymond, Nicolas'];Arch. Ration. Mech. Anal.,2016
2. Eigenvalues variation. I. Neumann problem for Sturm-Liouville operators;['Dauge, Monique', 'Helffer, Bernard'];J. Differ. Equations,1993
3. [3] Fournais, Søren; Helffer, Bernard Spectral methods in surface superconductivity, Progress in Nonlinear Differential Equations and their Applications, Tome 77, Birkhäuser, Boston, MA, 2010, xx+324 pages
4. [4] Helffer, Bernard Spectral theory and its applications, Cambridge Studies in Advanced Mathematics, Tome 139, Cambridge University Press, Cambridge, 2013, vi+255 pages
5. [5] Hislop, Peter D.; Sigal, Israel Michael Introduction to spectral theory, Applied Mathematical Sciences, Tome 113, Springer, 1996, x+337 pages (With applications to Schrödinger operators)