With the departure of Simon Rattle, and Antonio Pappano not due to succeed him as chief conductor until this time next year, 2023-24 will be an interregnum for the London Symphony Orchestra. So it was the orchestra’s associate artist Barbara Hannigan who conducted the opening concert of its new season at the Barbican, a typical Hannigan programme that mixed works from the mainstream repertoire by Haydn and Strauss with less familiar music from the second half of the 20th century. But at least one of the modernist pieces is already on the way to becoming a classic. Ligeti’s Ramifications, which generates shifting hazes of sound from two groups of strings tuned a quarter tone apart, is a wonderful example of his fondness for ear-teasing illusion, and a perfect palate-cleansing concert opener. Hannigan followed it with music by her fellow Canadian Claude Vivier. His 1981 Hölderlin setting, Wo Bist Du Licht!, has the German poet’s words delivered with studied solemnity by a mezzo soprano (the wonderfully poised Fleur Barron) over churning string microtones and tolling bells and gongs, while recordings of 20th-century news events – Martin Luther King’s I Have a Dream speech, the Robert Kennedy assassination, the Vietnam war – are heard in the background, all inhabiting a haunting, strange world of its own. An early Haydn symphony, No 26 in D minor, Lamentatione, continued that unsettling sense of something unresolved, though the performance was trim enough, without perhaps seeming as urgent and insistent as it might have been. But at the end of the concert a superbly delivered account of Strauss’s tone poem Death and Transfiguration made that theme of travelling from darkness into light explicit, with Hannigan and the orchestra bringing a consoling warmth to its final pages. And before it came another brief 20th-century rarity – Luigi Nono’s Djamila Boupacha, his 1962 tribute to the activist who had been imprisoned and tortured by the French during the Algerian war of independence; it’s a soaring, swooping soprano solo, which Hannigan delivered from the podium with radiant ease before plunging straight into the Strauss.